Montas exited Sunday's game against the Mariners due to tightness in the back of his shoulder, Martin Gallegos of MLB.com reports.
Montas was removed from Sunday's matchup after just one inning, and manager Mark Kotsay said after the game that the right-hander had trouble getting extended. The 29-year-old has been initially diagnosed with inflammation, but he's considered day-to-day for now. If Montas is cleared to make his next turn through the rotation, he tentatively lines up to start at home against the Astros on Saturday.