Manager Joe Maddon doesn't believe the injury is serious and expects Montero will play in Thursday's series finale against the Cleveland Indians.
The Cubs also placed left-hander Zac Rosscup on the 15-day disabled list with shoulder inflammation.
Rosscup is 2-1 with a 4.30 ERA in 26 relief appearances. He pitched the ninth inning of Tuesday night's game against the Cleveland Indians, but left after facing three batters with shoulder tightness.
Right-hander Yoervis Medina was recalled from Triple-A Iowa. He was acquired from Seattle for catcher Welington Castillo on May 19. Medina was 1-0 with one save and a 3.00 ERA in 12 relief outings for Seattle prior to the trade.