Manchester United captain Nemanja Vidic has ruptured his cruciate ligament and faces months on the sidelines, according to his agent Silvano Martino.
Vidic, 30, suffered the injury during United's 2-1 Champions League defeat to Basel on Wednesday, a result that saw the Red Devils knocked out of the competition at the group stage for the first time in six years.
The Serbia defender was carried off the St. Jakob-Park pitch on a stretcher after colliding with Marco Streller during the first-half and appeared to be in agony as he signalled to the bench that he needed to be immediately substituted.
Vidic later left the stadium on crutches and United boss Sir Alex Ferguson admitted after the game that the injury "looked a bad one at the time".
Now it seems Ferguson may have to do without his captain for a number of months, after Martino claimed Vidic's problem is very serious.
"Unfortunately he has suffered a ruptured cruciate ligament," Martina told Italian football website calciomercato.com.
Asked if his client would be out for several months, Martino replied: "Unfortunately so, yes."
A long-term absence for Vidic would be a nightmare scenario for United, who have conceded just three goals when he has played this season - compared to 19 goals in 14 games without him.
Ferguson is likely to call on Phil Jones to play in Vidic's stead alongside Rio Ferdinand for Wolves' visit to Old Trafford this weekend, with Jonny Evans and Chris Smalling also able to fill in at centre-back.