ANAHEIM — A’s second baseman Scott Sizemore sprained his surgically-repaired left knee in Tuesday’s game in Anaheim and will return to the Bay Area on Wednesday to undergo an MRI.

Both Sizemore and his employers are holding out hope that the injury is minor, but with Josh Reddick also out nursing a sprained right wrist, the A’s have no choice but to place one of them — likely Sizemore — on the disabled list on Wednesday in order to ensure enough healthy bodies are on their bench.

Once they do so, Andy Parrino will be promoted, MLB.com has learned. The versatile infielder/outfielder, brought over the offseason trade that sent Tyson Ross to the Padres, enjoyed a nice spring with the A’s and was batting .174 (4-for-23) in six games with the River Cats through Tuesday.

Parrino hit .207 with one homer and six RBIs in 55 games with San Diego last year, appearing in 26 games at shortstop and 15 at second base, while also playing two games at third and one in right field.

Sizemore suffered the injury in the fourth inning of Tuesday’s contest while chasing after a fly ball off the bat of Mike Trout that fell in for a hit. He immediately exited the game and was replaced by Eric Sogard.

“I just kind of stopped, kind of with a straight leg, and it didn’t feel right,” Sizemore said. “It kind of tightened up on me, so obviously being safe than sorry we’ll get it checked out tomorrow and hopefully it’s something minor and won’t be anything too serious. But, as of now, we don’t know anything.”

Sizemore underwent surgery on that same knee just last spring as a result of a torn ACL, forcing him to miss all of 2012. Tuesday marked just his second appearance of the season.

Best-case scenario, Sizemore learns Wednesday that the pain is stemming from scar-tissue tearing.

“That would be good,” he said, “but at this point it’s just kind of all speculation, so we just wish for the best.”

ANAHEIM — Josh Reddick expressed improvement in his sprained right wrist on Tuesday, but the A’s outfielder remains day to day and is unlikely to play in the club’s three-game series in Anaheim.

Manager Bob Melvin wasn’t ready to say as much Tuesday afternoon, but he didn’t have to. Reddick won’t attempt to pick up a bat until Wednesday, making even the possibility of a Thursday return ambitious. Friday, it seems, could potentially be the soonest he makes his way back to right field.

“He’s pretty quick to recover,” Melvin said. “We’re literally day to day. Whether it’s a couple days, whether it’s this series, whether he’s all right tomorrow, I really don’t know yet.”

In the meantime, Melvin said he will rely on Chris Young to handle right-field duties, giving the A’s an outfield of three true center fielders, with Yoenis Cespedes in left and Coco Crisp in center.

“When things like this pop up,” he said, “you realize why the front office went out and got us the type of depth we do have.”

Still, the disabled list remains a faint idea, with Reddick not even thinking about it.

“I don’t see it happening,” he said.

Reddick was relieved by an encouraging visit with the team’s trainers on Tuesday and was simply going to continue to ice the wrist, still visibly swollen, and perhaps try a handful of range-of-motion and strength exercises later in the day.

“Then we’ll see where we’re at tomorrow,” he said.

Reddick initially suffered the injury Sunday in Houston, where his wrist felt the brunt of the impact when he crashed into a wall while trying to snag a ball in foul territory. He was immediately taken to a nearby hospital for X-rays, which proved negative.

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On the same day the Angels learned they’ll be without No. 1 starter Jered Weaver for a month, the A’s relayed encouraging information from the opposing dugout regarding their own ace.

Lefty Brett Anderson, who suffered a left thumb contusion during his Sunday start against the Astros, is “in good shape” to make his next scheduled outing at home on Saturday against the Tigers, manager Bob Melvin said.

“He’s going to play catch today and if everything goes well, I don’t see why he wouldn’t throw his normal bullpen a couple of days after that,” Melvin said. “It’s a little bit sore, but he does get an extra day, anyway.”

Anderson can thank Monday’s off-day for that. He’ll now be able to push back his bullpen session by a day and start on five days’ rest rather than four.

The A’s southpaw underwent X-rays that came out negative at a Houston hospital immediately after completing his sixth inning on Sunday, four frames after he hurt his thumb. Knowing he was able to pitch with the injury and match a career high in strikeouts (10) along the way, the A’s were never too concerned about the hurler but simply wanted to act out of precautionary measures.

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A’s rehabbing infielders Hiro Nakajima and Adam Rosales are making encouraging strides in their respective rehabs back in the Bay Area, manager Bob Melvin said Tuesday.

Nakajima, nursing a strained left hamstring back to health, has begun taking swings in the cage and, on Monday, he even endured a few 40-yard sprints.

“He’s starting to feel that much better,” Melvin said, “so my guess is that once we get home he might be able to get out on the field with us and do all the normal pregame activities.”

The A’s return home from a six-game road swing on Friday, and should Nakajima be ready to participate in full baseball activity, the club can then begin deciphering potential timetables, including when to send him out for a Minor League rehab assignment.

Still, when Nakajima is deemed 100 percent, he’s not guaranteed a spot on the A’s roster — not while Jed Lowrie remains fully healthy himself and continues raking at the plate, where he entered the day batting .500 through the first seven games.

Rosales, meanwhile, has also started taking swings and playing catch, after being limited in activity by an intercostal strain. He, too, will likely play in a few Minor League games before the A’s decide whether to bring him back immediately.

HOUSTON — Josh Reddick’s all-out style of play typically harms his opponents more than it does his own body. That wasn’t so much the case on Sunday, though.

The A’s outfielder suffered a right wrist sprain in the fifth inning of his team’s game against the Astros, after crashing into a wall in foul territory at Minute Maid Park while attempting to make a catch.

Ball never made it into glove, and Reddick was immediately seen cradling his right arm, before he eventually exited the game with a trainer by his side. He was sent to a nearby hospital for X-rays, which fortunately proved to be negative.

“It was a huge sigh of relief,” Reddick said. “I was scared. I was nervous that something was seriously wrong because I lost feeling in that area for quite awhile. I never lost feeling in the fingers, which I knew was a good sign.  But for as hard as that wall is with all that metal wiring, I was really nervous about how serious it was going to be.”

So were his manager and teammates.

“I was very concerned,” manager Bob Melvin said. “It takes a lot to get him out of the game. But I feel much better about it now. I don’t know what the timetable is going to be, but the fact that it’s not broken, based on how it was feeling originally, is good news.”

The A’s have deemed Reddick day-to-day but aren’t certain whether to consider him a candidate for the disabled list at the moment. At the very least, they know he likely won’t play Tuesday’s opener in Anaheim.

In the meantime, Oakland has an abundance of outfield depth, with Chris Young and Seth Smith able to keep Reddick’s spot warm while he’s out.

“We’ll just keep icing it and see where we are on Tuesday,” Reddick said. “Obviously I don’t want to miss any time. The numbers don’t show I’m doing very well, but I’m hitting the ball hard and having great at-bats, so I can’t be too upset about that. I’ll keep grinding and things will work out.”

Reddick exited the day with a .125 average. But he’s not the only one struggling — Yoenis Cespedes and Josh Donaldson are both hitting .120 — and his Gold Glove-winning defensive skills are valued just as much by the A’s, who weren’t at all surprised to see him make such a determined attempt at Marwin Gonzalez’s foul fly ball despite leading by eight runs at the time.

“You never want to see anyone come out of the game like that,” starter Brett Anderson said, “but as a pitcher you applaud his effort.”

“It doesn’t matter the score, I’m always playing hard, and I’m not going to change that just because we’re up, 10-0,” Reddick said. “It never goes through my mind to not run hard.

HOUSTON — As he assured Saturday night despite a mid-game elbow issue, Yoenis Cespedes is just fine. But he was given the day off, anyway, Sunday, amid struggles at the plate.

Cespedes is 0-for-9 with five strikeouts in the series, and he has just three hits total — two are home runs — spanning 23 at-bats during the first six games of the season.

“He’s just pulling off the ball a little bit,” manager Bob Melvin said Sunday morning. “Sometimes he tries to do a little too much and pulls off the ball some. He certainly doesn’t need to because he can hit the ball out of the ballpark anywhere, but sometimes a day off can distance you from that.”

Cespedes will actually get two days, with the A’s set to enjoy a scheduled off-day in Anaheim on Monday, though Melvin said he remains a pinch-hit option off the bench.

Naturally, there’s really no significant concern over Cespedes’ slow start. The slugger proved last year, while playing in the Majors for the first time, that making adjustments is something of a specialty of his.

“He not only adjusted game to game but during the middle of an at-bat,” Melvin said. “When he’s going good, he’s thinking that way all the time and able to make adjustments. He’s just off to a little bit of a slow start, but even so he’s had some instrumental hits that have helped us win games. We don’t worry about him too much.”

Cespedes hardly ever expresses such sentiments, either. On Saturday, he told reporters, “Don’t worry, I’m going to give you guys a lot of home runs this year.”

Upon hearing this Sunday morning, Melvin smiled.

“The one thing about him is that [his struggles] are never for a lack of confidence,” he said. “He’s never a guy that gets down and doubts himself. He just gets mad and sometimes frustrated but it’s not like he’s ever worried about who he is.”

With Cespedes out of action on Sunday, Melvin was able to get Seth Smith his first start in the outfield. He also plugged Chris Young into center field, allowing Coco Crisp a day to play the role of designated hitter.

“We want to keep Seth current in the outfield,” Melvin said. “We have a lot of moving parts, and at times it’s a serious benefit. Coco plays really hard and, at times, gets nicked up. We can combat those nagging injuries with the DH role.”

SAN FRANCISCO — The A’s have 12 relievers on their roster and just three more days to narrow that field to seven.

“That’s a good problem to have, yet there will probably be a few guys that deserve to make the team that don’t,” manager Bob Melvin said. “There’s usually a couple of guys every year where that’s the case but probably a few more this year, based on the depth that we do have in the bullpen. The last few cuts will be difficult.”

But perhaps the actual decisions won’t be. Closer Grant Balfour and his set-up men, Ryan Cook and Sean Doolittle, are locks to make the team. That leaves four open spots, and there just so happens to be four relievers — good ones — who are out of options.

That group includes lefties Jerry Blevins and Travis Blackley and right-handers Chris Resop and Pat Neshek. Blevins’ spot is seemingly secure, and Resop and Neshek don’t have much to worry about, either, especially after producing zero ERAs this spring. Blackley, meanwhile, has a 14.21 mark, though his contributions to the 2012 club may end up outweighing those struggles when it comes down to decision time.

“Options always come into play,” Melvin admitted. “That doesn’t mean that that’s the way it’s going to go, but certainly when you do have depth and you try to keep everyone in the fold that sometimes happens. Whether that’s the case here I’m not sure yet.”

Blackley is perhaps the most versatile of any pitcher on the A’s roster, having pitched effectively as both a starter and reliever for the team last year. Should he make the team, he’d be mostly used in a long-relief role. Melvin said Thursday that he’s not committed to carrying a long reliever but hinted that the job could be done by several other guys in the event Blackley is not on the team. He dropped the names of Pedro Figueroa, Jordan Norberto, Evan Scribner and non-roster invitee Mike Ekstrom — who, like Hideki Okajima, could all be the odd men out.

Of Blackley, he said this: “He hasn’t pitched as well as he’d like to this spring, but he did do some very good things for us last year, whether it was starting or long relief, so that plays into it.”

Ultimately, “we have a pretty good idea, other than maybe one spot,” Melvin said, before adding, “Maybe two, but maybe closer to one. One and a half. Let’s leave it at that.

“It could come down to some performances these last three days.”

SAN FRANCISCO — While it’s not yet known whether shortstop Hiro Nakajima will require a trip to the disabled list for his left hamstring strain, the A’s are at least certain he won’t play in this weekend’s three-game exhibition series against the Giants.

The A’s ventured across the Bay Bridge for the first game of the series on Thursday, and it was during that time Nakajima was scheduled to be seen by the team’s doctors to determine the next course of action.

“I do know he will not play in this series, and then after that I’m not 100 percent sure,” manager Bob Melvin said at AT&T Park, “but I’ll probably have a better indication after the game.”

Uncertainty not only surrounds Nakajima’s health but his ability to compete in the big leagues. The Japanese shortstop struggled all spring, both on defense and at the plate, and his slow progression has cleared the way for Jed Lowrie to take over everyday shortstop duties.

The A’s aren’t yet ready to say as much, but there’s no denying that his injury only adds to an already difficult adjustment period. For now, though, they’re not ruling him out of the opening series against the Mariners that begins Monday. Even if healthy, Nakajima could be sent to the Minors to pick up more at-bats.

“It’s tough to say, it is,” Melvin said. “If he misses three games here and a couple back there, it would be difficult to get back into the swing of things, but I’m not really sure yet.”

Once bountiful in number, A’s middle infielders are dropping like flies.

Oakland entered Tuesday with as many as six players vying for spots in the heart of the diamond and left it with only four of them healthy.

Just hours after announcing that Adam Rosales would start the season on the disabled list, the A’s watched shortstop Hiro Nakajima exit the 10th inning of a road game against the Indians with a left hamstring strain. He’s considered day to day.

“It’s too bad,” manager Bob Melvin said. “Hopefully it’s nothing significant and he’ll be back playing in a few days, but you don’t know with hamstrings. They can be difficult injuries.”

Nakajima suffered the injury while running from first to second on a sacrifice bunt, just minutes after he had found his way out of a 0-for-20 slump with a base hit. He motioned for a trainer and walked off the field with a slight limp under his own power, ultimately deferring questions from the media before getting on the team bus.

The struggling infielder’s murky health status only makes it that much more plausible that he doesn’t begin the year on the A’s 25-man roster. Rather, Jed Lowrie is likely to begin the season as the everyday shortstop, with Scott Sizemore and Eric Sogard sharing duties at second base. Andy Parrino, who is still in camp, is expected to start the year in Triple-A Sacramento.

That’s where Nakajima seems destined to pick up more at-bats before making his Major League debut. Should his injury prove to be anything but minor, the A’s could place him on the 15-day disabled list and have him rehab with the River Cats. Or, they can simply option him there before setting their roster.

Healthy or not, Nakajima still has work to do. He’s batting .167.

“He was working on some stuff in batting practice today, trying to use his back side and get his legs more involved,” Melvin said. “He had a good BP today and took a good swing on that one there in the 10th, so maybe he’s making progress, finding something that’s working for him.”

With news of an injury to infield candidate Adam Rosales coming out Tuesday, the A’s roster is suddenly taking shape.

The versatile Rosales, out of options and in good position to grab a roster spot, will instead open the season on the 15-day disabled list with a left intercostal strain. It’s likely, then, that it will be a mix of Jed Lowrie, Scott Sizemore and Eric Sogard commandeering the middle infield come Opening Day.

Lowrie has been too good this spring — he carried a .310 average into Tuesday — to not be awarded an everyday role with the A’s, who will probably give shortstop Hiro Nakajima more at-bats in the Minors before introducing him to the big leagues.

That leaves the right-handed hitting Sizemore and left-handed Sogard to form what could be a nice platoon at second base, where Rosales was also fighting for playing time.

The 29-year-old Rosales, injured in Monday’s game, was batting .324 with three home runs and nine RBIs in 21 games this spring. This marks the second time in three years he will begin the season on the DL, having sat out the start of 2011 while recovering from a fractured right foot.

The recovery time for intercostal strains vary, but typically players require at least a month off before returning to game action.

Tuesday’s news bodes well for first baseman Nate Freiman, whose chances of making the team have grown now that Rosales — a backup option at first base — is out of the mix.

Three A’s players were hit by a pitch in as many innings on Sunday, and one felt worse than the others.

Second baseman Scott Sizemore suffered a left hand bruise in his third at-bat against Rockies right-hander Tyler Chatwood, and he was taken out the next inning when he experienced trouble getting a good grip on the bat.

Sizemore was seen leaving the A’s clubhouse with his left hand wrapped, though he said in passing that it was “nothing too serious,” or at least he hoped.

Manager Bob Melvin also wants to believe that’s the case, telling reporters that it “didn’t look like a fracture” but, rather, a minor soft-tissue injury. The A’s will wait until swelling subsides in Sizemore’s hand and determine Monday morning if he needs to undergo an X-ray.

The infielder has already had one too many tough breaks in his young career, missing all of 2012 while rehabbing from a torn ACL just two years after a broken ankle derailed his rookie season with the Tigers.

“He’s a tough kid,” Melvin said. “He’s had a couple of tough injuries in the last four years and that’s the last thing you want to see happen, but hopefully it’s nothing too serious.”

Sizemore is in battle, primarily with Jemile Weeks, for the second-base job, and he did his part Sunday by notching two hits in his first two at-bats, after collecting just one in his previous 10 at-bats.

“He’s working hard, hadn’t gotten many results, even though he was hitting some balls hard,” Melvin said, “and so it’s always nice to get a couple of hits and feeling good about staying with the plan that you have.”

A’s manager Bob Melvin came with news Thursday morning, and he didn’t waste any time delivering it.

“Let’s go ahead and say Brett Anderson is our Opening Day starter,” Melvin said, smiling.

The news isn’t so much surprising as it is rewarding for the 25-year-old Anderson, who is entering his fifth season with the A’s.

Thrust into a playoff run upon his August return from Tommy John rehab last year, the southpaw responded beautifully, winning his first four starts while posting a miniscule 0.69 ERA while walking just three in 26 innings.

Anderson lost his next two starts and suffered an ill-timed oblique strain, before making a seemingly miraculous comeback in short time to pitch Game 3 of the American League Division Series. He allowed two hits in six shutout innings in Oakland’s 2-0 win over the Tigers, saving the team from elimination.

“Based on the guys that we have and how successfully he came back for us last year, we really feel like he’s the man to lead the staff,” Melvin said. “He worked hard to get back and put himself in a position to compete with us at a time of the season where there’s no easing into things. You gotta be good right away, and he was. Then he gets hurt and we think he’s done, and he works just as hard to get back and pitch in a playoff game.”

Though limited to 38 starts over the last three seasons due to four stints on the disabled list, Anderson finally appears primed to compile at least 30 this year, so long as good health remains on his side. To that end, Anderson put in hours of work to allow for such endurance, shedding 25 pounds during his rehab and keeping off the weight this winter.

“There’s never a better time to change when you can’t do anything else,” Anderson said earlier this month. “It’s never fun to be hurt for an extended period of time, but in my case it was probably a blessing in disguise, where it took something like that to realize I should probably make some changes.”

Anderson will be making his spring debut Thursday against the Cubs, and he jokingly asked Melvin if he was sure he wanted to openly announce Opening Day plans without having seen the lefty pitch in a game.

“To say he jumped up and down and all that, probably not, but he took it in stride,” Melvin said of the mellow Anderson. “He said, ‘Every guy aspires to be an Opening Day starter,’ so he was excited, as excited as he gets.”

Anderson is expected to be followed in the rotation by Jarrod Parker, Tommy Milone, A.J. Griffin and Dan Straily — all 26 years old or younger. Veteran Bartolo Colon, who still has five games remaining on his drug suspension, is eligible to rejoin the team after the first week of the season.

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In other news, A’s closer Grant Balfour (right knee) is scheduled to see a doctor today. He made 35 throws from flat ground on Wednesday, and his next step could be throwing off a mound, should his doctor give him the green light.

Michael Ynoa threw a bullpen yesterday, and he’ll throw one more before facing live batting practice. That doesn’t put him too far off from game action.