Montas (shoulder) is slated to undergo an MRI in Oakland on Monday, Martin Gallegos of MLB.com reports.
The right-hander experienced tightness behind his right shoulder in Sunday's brief 13-pitch start against the Mariners, with manager Mark Kotsay noting Montas couldn't get "fully extended" on his pitches. Consequently, a Monday MRI has already been ordered up, and the results should offer further clarity on Montas' chances of making his next scheduled start against the Astros on Saturday.