Backes played 11:20 before leaving the game after he was involved in a collision with Senators forward Colin Greening. Following the hit he struggled to make his way back to the Blues' bench and immediately went to the locker room.
His last shift came with 2:49 to play in the second period.
Backes is off to one of the best starts of his career and in 31 games this season has scored 16 goals to go with 14 assists.
The concern for the Blues has to be that Backes has suffered concussion in his career but returned to the lineup just a few days later.