The Tigers optioned Montero to Triple-A Toledo on Saturday.
The 25-year-old righty will be pushed out of the big-league rotation following Tarik Skubal's return from the paternity list. Montero will aim to turn things around in the minors after a poor start to the second half, as he's surrendered 10 runs (nine earned) across just 8.1 innings over his last two starts.