Ellis, 32, is in the middle of a gradual rehab program put together by A's strength and conditioning coach Bob Alejo. The veteran infielder, who is rehabbing a strained left hamstring in Phoenix, has begun hitting off a tee but has yet to face pitchers.
Once past that step, Ellis will likely be given a Minor League rehab assignment, but there is currently no timetable for his return.
"The good news is that he's doing better every day and is now doing baseball activity," manager Bob Geren said Tuesday. "He'll need to make sure he can swing at game speed, so he would have to be put to that test before he's ready."
Ellis is currently in the midst of his fifth career stint on the DL, where he was placed April 21 after leaving the previous day's game following just five innings of work. He had missed seven games with the injury from April 12-18.