Alejandro Faurlin is set to miss a large part of the season after the QPR midfielder suffered an anterior cruciate ligament injury in Wednesday's Capital One Cup defeat at Burton.
The 28-year-old has sustained two similar injuries over the last three seasons and will now be missing from Harry Redknapp's squad for a number of months.
Faurlin penned a new one-year deal at Loftus Road in July having spent a portion of last season on loan at Palermo in an attempt to improve his fitness.
R's boss Harry Redknapp, who may now look for another midfielder before the transfer window shuts on Monday, said the club will do all they can to help the player recover once again.
"We're all desperately saddened and disappointed for Ale," he said. "He is a great man and player, and he's suffered terribly bad luck over the last few years with injuries.
"We will, of course, do everything we can to support him and help him back on the road to recovery."
Faurlin started QPR's opening Barclays Premier League defeat at home to Hull before coming off the bench in the 4-0 loss to London rivals Tottenham last weekend.
He was included in a much-changed starting line-up for the second round Capital One Cup tie at Burton, which the Sky Bet League Two side won 1-0, but that could yet prove to be his last match of the season if the injury takes the full nine months to recover from.
QPR's head of medical services, Peter Florida James, told www.qpr.co.uk: "We're all absolutely devastated for Ale.
"It looked so innocuous on Wednesday night, so this has come as a massive blow for us all.
"The knee itself stayed pretty stable, but the scans have since revealed his ACL graft has ruptured. If he has a repair it will be a six to nine month injury, which is absolutely devastating for all concerned."
Faurlin originally moved to Loftus Road from Argentinian second division side Instituto de Cordoba in 2009 and, despite suffering two previous ACL injuries, has gone on to play 121 league games for the Hoops.