OAKLAND -- In an expected move, the A's on Tuesday placed first baseman Daric Barton on the 15-day disabled list, as he continues to strengthen his surgically repaired right shoulder.

The 26-year-old infielder had yet to play in consecutive games at first base and was unlikely to do so by the time Oakland reopens the regular season Friday against the Mariners.

"We just felt like he needed, and he felt like he needed, several games in a row to feel good about where his arm strength is," manager Bob Melvin said.

Thanks to the A's early season start in Japan, the team can backdate Barton's DL stint to March 24, meaning he's eligible to be reinstated as early as April 8. That's an off-day for Oakland, so he could make his season debut the next day at home against the Royals, "but we'll see where his progress takes him to that point," Melvin noted.

In the meantime, Melvin is expected to enter the season with both Brandon Allen and Kila Ka'aihue on the 25-man roster. The A's currently have 26 active players on the 40-man roster and must cut that number to 25 by Wednesday's 1 p.m. PT deadline. It's likely that probable fifth starter Graham Godfrey -- not needed for a start until April 16 -- will be optioned to Triple-A Sacramento to round out the roster.

Allen, who started Tuesday's exhibition contest against the visiting Giants, entered the day batting .303 with two home runs and 13 RBIs this spring. Ka'aihue has three homers to his name but is hitting just .222 with a .256 on-base percentage.

"I think each of them has done some things that would merit being a starter," Melvin said. "Both, at times, have played defense nicely for us, so it's probably a good, tough decision to make and, based on where we are right now, it looks as if both would be on the Opening Day roster."

Braden has injection, recovery pushed back

OAKLAND -- A's starter Dallas Braden will be shut down for three weeks after receiving a platelet-rich plasma injection in his surgically repaired left shoulder Monday.

Dr. David Altcheck, who performed Braden's shoulder capsule procedure last May, administered the shot and recommended the downtime to relieve the strain in the pitcher's shoulder.

Before Braden's setback, suffered the day after a bullpen session in Arizona while the club was in Japan, the A's had hoped to welcome him back in the rotation at the beginning of May. Now, June may be a more realistic timeline, considering Braden will have to restart his throwing program once cleared to do so.

For the time being, he's limited to strengthening activities.

"The schedule he was on, obviously we're not on any more," manager Bob Melvin said. "We're not even looking at a schedule right now, just seeing how he feels."

Braden is nearly 11 months removed from his surgery, one familiar to Mets left-hander Johan Santana, who needed 18 months to recover from a similar procedure. Santana, who last pitched in a Major League game Sept. 2, 2010, is scheduled to be New York's Opening Day starter Thursday.

Worth noting

• Reliever Joey Devine, sidelined yet again by a case of right elbow tendinitis, is awaiting results on an MRI he underwent Monday. Those results are expected to reveal further information on the righty's sore elbow.

• Rehabbing lefty Brett Anderson threw a 40-pitch bullpen session Tuesday afternoon and has begun adding curves and sliders to his mix.

"I think he looks as good as he can look at this point in time," Melvin said. "From the day he started throwing off the mound, it looked like this wasn't an arm rehab guy. He's looked terrific. He's at a great pace right now. We don't want to push him, obviously, but he's doing as well as you'd expect."

• Shortstop Cliff Pennington, who exited Monday's exhibition in the second inning because of tightness in his left groin, was held out of Tuesday's lineup but said he felt 100 percent and, if in season, would be playing. There's no need to rush the infielder, though, and Melvin said he would make a decision on Pennington's availability for Wednesday later in the evening.