The Blues record signing only returned to the side in last weekends local derby game against the Villa after almost a month out with hamstring problems but Bruce fears that the way he pulled up in the game against Sunderland could mean him spending a lot longer than that on the sidelines this time.
“It looks like a bad one,” said Bruce after the game on wednesday night.
“We should know more in the next day or two but when somebody pulls up like that you fear the worst.
“It was his hamstring which we thought he’d overcome.”