MILAN, Italy — Ronaldo traveled to Paris today for an operation to repair the ruptured tendon in his left knee, an injury that could end his career.

The three-time FIFA world player of the year was injured in AC Milan's 1-1 draw with Livorno in the Serie A on Wednesday.

"He fears for his career," Milan president Silvio Berlusconi told Italian state RAI TV. "I called him last evening and told him to believe in himself. He has enormous physical potential. This morning, he was going to France for an operation.

"As a 31-year-old, he's very young. He has an extraordinary physique, and I think within a few months he could return to being the champion that we all know him as."

This latest injury occurred two minutes after Ronaldo entered the game during a play that earned Milan an equalizing penalty. The Brazilian was carried off the field crying.

In Paris, Ronaldo is expected to see Gerard Saillant, the same surgeon who treated him for a similar injury to his right knee in 2000. Ronaldo will undergo surgery at the Pitie-Salpetriere Hospital.

"He will be operated on this evening or overnight by Eric Rolland, my successor at Pitie-Salpetriere. I will help him," Saillant told The Associated Press by telephone Thursday. "It appears that it is the same injury that he had previously. If this is the case, an operation is obligatory."

After the previous operation, Ronaldo needed more than a year to return to competition, Saillant said.

"Considering his age, with eight more years on him, it is hard to say" when he could return to play, Saillant said.

Ronaldo has battled serious injuries throughout his career, and has played sparingly since joining Milan from Real Madrid in January 2007.

Wednesday's match was only his fifth in Serie A this season after injuring his thigh during preseason training on July 31. He returned in November, but has been on and off the roster due to a series of recurring problems.