The Blues skipper was substituted ten minutes from the end of the 5-0 home win against Portsmouth on Saturday having aggravated the groin injury that he had sustained in last weekends game at Charlton.
Cunningham's injury could not have come at a worse time for Bruce who will be without the suspended Matthew Upson for the FA Cup 4th Round tie at Reading on Saturday whilst Martin Taylor is still struggling with the foot injury he picked up in the game at Charlton.