Ronaldo. the AC Milan striker is likely to be ruled out for nine months after undergoing surgery on his left knee.

The 31-year-old had an operation to repair a ruptured tendon in his knee in Paris on Thursday, after he was carried off during Milan's 1-1 Serie A draw with Livorno on Wednesday.

Ronaldo’s spell at the club has been blighted by injury since he joined from Real Madrid in January last year and Wednesday night's appearance was only his fifth this season. The three-time World Player of the Year and two-time World Cup Winner has not signed a fresh contract with Milan, and his deal expires in June.

Carlo Ancelotti, Milan’s coach, said: “Now everything is in his hands. I am convinced Ronaldo will return to playing because football is his world and we will wait for him.

“The first time he had this type of injury, to the left knee, he recovered perfectly. I don’t see why he shouldn’t manage this time.”

Adriano Galliani, AC Milan’s chief executive, was also optimistic that Ronaldo would recover. He said: “We hope this very sad image on Wednesday is not the last we see of him on the field.

“Ronaldo is still not 32 and even if I don’t comment because I am not a doctor, I hope he returns to play and that he does so in our jersey. Ronaldo is perhaps the best player Brazil have had since Pele.”

Dr. Gerard Saillant, who participated in the surgery, said it had been successful.