Abbiati underwent tests in Antwerp today which have revealed the extent of the injury sustained during yesterday's game at Siena.

A statement from the club read: "The test done on Abbiati have confirmed the initial diagnosis and the complex injury he sustained. Abbiati will need two to three weeks of rehabilitation before returning back to Belgium where he will undergo surgery."

Abbiati was substituted early in the first-half of his team's 5-1 Serie A victory at Siena yesterday.

The Italian goalkeeper had been Carlo Ancelotti's preferred choice in goal this season, with Brazilian goalkeeper Dida his understudy.

The Rossoneri, who are already without injured duo Gennaro Gattuso and Kakha Kaladze for the rest of the campaign, have been left reeling by another serious injury.

"The series of injuries we have had this season has been incredible," said captain Paolo Maldini. "I am saddened for a player like Christian, who has shown his value.

"At the beginning we thought it was just a knock but then he felt pain in his knee.

"It's a real shame because Abbiati has had a great campaign so far."

AC Milan vice-president Adriano Galliani could only look at the positives.

"Fortunately, we have a luxury reserve goalkeeper in Dida," he said. "With Dida we have won so much."

The Rossoneri travel to the San Paolo to meet Napoli next weekend, sitting in third place with an eight-point advantage over fourth-placed Genoa.