Nottingham Forest boss Steve McClaren has been left "distraught" after Chris Cohen was ruled out for a year.
Midfielder Cohen, who has been mainly playing at left-back this term, suffered knee ligament damage in Saturday's 2-1 defeat by Derby County.
McClaren told BBC Radio Nottingham: "It's a big blow for us and the club but a bigger blow for him because he's been our top performer this season."
Forest have already moved to bring in QPR defender Clint Hill.
But McClaren said Cohen would be sorely missed: "I was distraught when it happened and distraught when I found out the results.
"He has to take nearly a year out but he'll be back and he'll be stronger and better, but we'll miss him."
Cohen, who has played most of his career in midfield but has started the season at full-back, limped off during the loss against Forest's fierce rivals.