Troubled Spanish giants Barcelona announced on Monday afternoon that Gabriel Milito would be out of action for around six months, dpa reported.
Ricard Pruna, head of the Barca medical team, told the media that Milito's right knee, which was operated upon in Argentina in 2001, showed signs of "instability", and that the cruciate ligament "is not following the line that it should."
Milito, 27, will be operated upon as soon as possible.
The Argentine defender felt pain in his right knee during last Tuesday's 1-0 Champions League defeat away to Manchester United.
Curiously, Milito was going to sign for Real Madrid from Independiente in July 2003, only for the Real doctors to reject the deal because of concerns about his right knee.
Milito hardly suffered any injuries during his four seasons at Zaragoza, who sold him to Barcelona in July 2007.