QPR have confirmed Alejandro Faurlin will be out for at least six months after injuring the anterior cruciate ligament in his left leg.
The midfielder fell awkwardly during Saturday's home win over Derby County and was forced to leave the field on a stretcher.
Subsequent scans have confirmed QPR's worst fears and Faurlin, who suffered a ruptured cruciate ligament in his right knee in January 2012, now appears certain to miss the remainder of the Championship campaign.
The Rs' head of medical services, Peter Florida James, told the club's official website: "It's a really nasty cruciate injury.
"We're all desperately disappointed for Ali but he is a great professional and I'm sure he'll work just as hard at recovering from this injury as he did from his previous ACL rupture."
Faurlin has made nine appearances this season for QPR, who sit third in the Championship.