Montgomery suffered a concussion during Sunday's 24-17 loss to the Titans, Jason Lieser of the Chicago Sun-Times reports.
Montgomery got shaken up in the fourth quarter of Sunday's loss, prior to which he had 14 carries for 30 yards and three catches for 12 yards (on three targets). The second-year pro now will need to clear the league's five-step concussion protocol before retaking the field, which puts his availability for Week 10's Monday Night Football contest against the Vikings in some jeopardy. With Tarik Cohen (knee) already out for the year with a torn ACL, the Bears only have Cordarrelle Patterson, Ryan Nall and Artavis Pierce behind Montgomery.