The Argentinian was initially expected to be sidelined for just six months with a damaged ligament, but surgery to correct the problem revealed a complete tear.

The defender picked up the injury in Barca's Champions League semi-final second-leg defeat against Manchester United last month.

Surgeon Ramon Cugat told a news conference: "First we carried out arthroscopic surgery on the right knee and discovered that effectively the ligament was broken, so we proceeded to extract tendon from the left knee to incorporate it into the damaged one.

"Normally an operation on the anterior cruciate ligament would entail a six month layoff.

"In this case, we have replaced one ligament that was operated on seven years ago...and put in a new one.

"The six months could stretch to nine as this type of operation could have more complications."

Milito, who suffered a similar injury in 2001, joined Barcelona from Real Zaragoza last July for a fee which could rise to 20.5million euros.