AC Milan striker Ronaldo is facing a lengthy spell on the sidelines after rupturing tendons in his knee during the 1-1 draw with Livorno on Wednesday.

The 31-year-old was carried off with an injury to his left knee just three minutes after coming on as a substitute at the San Siro.

Early estimates suggest the Brazilian, who has suffered a succession of serious knee injuries throughout his career, will be out for between nine months and a year.

Coach Carlo Ancelotti downplayed fears the injury could end Ronaldo’s career.

He told the club’s official website: “We are all very upset and worried about what happened to Ronaldo.

“I don’t think I can say that his career is over because only time can tell when his career will end.

“For our part we can only be there for him and stay calm.

“His team-mates left the stadium in a hurry to go to the hospital and find out his condition.

“For us to be close to him is useful for him in such a delicate moment in his career.

“On Sunday he didn’t play well but yesterday in training he was good, he seemed more alert, with better reactions and more ready.

“It’s a pity because we value Ronie a lot, he has always played with great seriousness and great disposition.

“Ronie has always carried himself very well and has always looked to contribute to Milan.”

Milan head of medicine Jean Pierre Meersseman confirmed the extent of the player’s injury.

He said: “After Ronaldo’s injury we decided at once to transfer the player to the Galeazzi hospital in Milan.

“It is one of the best orthopaedic hospitals in Europe.

“There’s little to say about the seriousness of the injury - unfortunately they confirmed that it was a rupture to the tendons of his left knee.

“He will definitely need surgery.

“We are all distraught at what’s happened.”