Gallen was diagnosed with right hamstring tightness after he left Friday's game against the Giants.
Gallen was removed in the top of the third inning after he appeared to hurt himself during his pitch delivery. The right-hander will be evaluated in the coming days to determine his status, but it's not yet clear whether he'll be able to make his next turn through the rotation. If he's cleared to pitch, Gallen tentatively lines up to make his next start at home against the Rockies on Thursday.