Lewis McGugan is facing a spell on the sidelines after suffering a torn thigh muscle.
The Nottingham Forest midfielder has been in discomfort for a couple of weeks and has finally been forced to seek medical attention.
He underwent a scan earlier in the week, which revealed the full extent of the problem.
It remains unclear how long the 19-year-old will be out of action, but Colin Calderwood is wary of throwing the youngster back in too early.
"Lewis has got a slight tear in his rectus femoris and he's going to have to sit around for a short period," the Reds boss told the club's official website.
"It's something he may have picked up towards the end of pre-season, hence the fact he missed the Morecambe game (in the Carling Cup).
"He was in great pain after the Swansea game, where I think he played particularly well, and when we had it scanned this week there was a small tear at the top of his thigh.
"That becomes a problem - we've obviously got to shut him down because if it were to tear further or rip that would be a three-month injury."