The right-back dislocated his shoulder following an innocuous challenge during Tuesday night's win against Bolton.
It was only the third game that the on-loan Swindon man had made for the club since he made the switch to St. Andrew's.
The 24-year-old had excelled in all of those matches and it had been hoped that he would not require surgery and therefore miss just a month. But it is likely that he will need his shoulder pinned.
"It’s not good," said the Blues boss. "We’ve had a second opinion and we’re waiting for the response from that today but it’s pointing towards surgery which will mean a minimum of three months out.
"It’s a hammer blow following on from the hammer blow I’ve taken with Stephen Carr (knee surgery). We’ve had Carr, who I consider to be the best right-back in the division taken away from us for the majority of the season, but he’s also my leader.
"I found a replacement that was capable of filling those shoes and he did it extremely well. He was outstanding for those three games and then 'bang' we get news like this.
"It’s a tough one for us to take. I know the history of the position before my time here and it’s a bit of a cursed position. I’ve been on the phone over the last 24 hours in terms of looking into the loan market but not many managers want to loan me a right-back now!"
Although Clark has other players that could slot into the right-back position, he says the situation is not ideal over a longer period.
"That’s half the problem," he added. "If it was for the short term you might just get away with it, but because of the length of time it does help to try and have a recognised full-back. And certainly the type of full-back that can play the way I want them to play, which is in the Stephen Carr-Paul Caddis mould.
"I’ve been in conversations with Peter (Pannu) and the people behind the scenes. Obviously if we can find the right player to do the job I’ll imagine I’ll get the same backing that I’ve had since I came through the door, which has been everything I wanted and everything that I knew I would. Whichever player I’ve gone for we’ve ended up getting."