Montero was optioned to Triple-A Toledo on Saturday, Cody Stavenhagen of The Athletic reports.
The 24-year-old righty put together a decent spring, posting a 3.21 ERA, 1.29 WHP and 17: 6 K:BB in 14 innings, but Montero ultimately fell short in his bid for a roster spot. In light of this transaction, Casey Mize and Jackson Jobe appear locked in at the back of the rotation for Detroit.