AC Milan and Brazil striker Ronaldo has ruptured a ligament in his left knee and must undergo surgery. Ronaldo was carried off in tears after going down heavily during the 1-1 Serie A draw at home to Livorno last night.

The 31-year-old, who has hardly featured this season because of a series of injuries, had only come on as a substitute three minutes earlier.

Ronaldo sustained two serious injuries to his right knee while playing for Inter Milan in 1999 and 2000 but recovered to help Brazil win the 2002 World Cup. He went on to play for Real Madrid before joining AC Milan in January 2007.

"We're all very sad and worried about what happened to Ronaldo," said Milan coach Carlo Ancelotti. "I don't want to say his career is over because only time can put the word end to his career.

"From our part we can only stay close to him. His team mates left the stadium quickly to reach the hospital to check on his condition.

"I think it's the right way to stay close to a player who's suffering. Being close to him can help him cope at such a delicate moment of his career," added the Milan coach.