Montgomery was diagnosed with a rib injury during Sunday's game in Tampa Bay.
Montgomery was tackled from behind in the second quarter and needed medical attention on the field before going to the sideline and eventually the locker room. It's unclear if he'll be able to return, but if Montgomery doesn't, Craig Reynolds will be the Lions' primary runner for the rest of Week 6, with Devine Ozigbo the other healthy option due to Jahmyr Gibbs (hamstring) being inactive.