Manager Bryan Price said he will announce a starter to take Bailey's spot in the rotation as soon as Friday. Bailey was scheduled to pitch Saturday at Colorado.
Price said Bailey thought he hurt his elbow while batting in his last start Aug. 7. The veteran pitcher recently threw a light bullpen session, but it didn't feel any better.
Bailey underwent an MRI, which detected a flexor mass strain in his elbow.
There's no timetable for Bailey's return. Price said Thursday before the start of a series with Colorado that "the injury shouldn't be something that deprives him from pitching for us this year."
Bailey is 9-5 with a 3.71 ERA.