Thomas is dealing with inflammation in his right elbow and will start up a throwing program Monday, Martin Gallegos of MLB.com reports.
Thomas is still expected to see some Cactus League action as a designated hitter, but he'll need to build up his arm strength before being cleared to play the outfield. The 25-year-old is competing for a bench spot on the Opening Day roster after posting a .684 OPS in 49 games as a rookie last year.