He has been on the disabled list at Triple-A Las Vegas for the last three weeks with a strained left oblique.
Montero, 23, had allowed 9 runs in 8 innings in the three starts since being demoted by the Mets on May 31. He is expected to return to the rotation in Triple-A Las Vegas when he is activated from the disabled list.
Montero is considered one of the team's top pitching prospects, checking in at No. 85 on MLB.com's off-season list of top prospects in baseball.