Montgomery suffered a left knee injury during the fourth quarter of Sunday's game against the Lions, Dan Wiederer of the Chicago Tribune reports.
Montgomery was in visible discomfort while the training staff tended to his leg, and he later needed assistance to get off the field and to the locker room, according to Adam Jahns of The Athletic. The severity of the injury hasn't been revealed, but if he's unable to return, he'll end the game with 23 carries for 106 yards and two touchdowns.