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."