Brazil great Ronaldo flew to Paris on Thursday for surgery on a career-threatening injury sustained in AC Milan's Wednesday night Serie A game against Livorno.
He entered the city's famous Salpetriere Hospital at about 14:00 local time (12:00 GMT) for an operation that was expected to take about two hours.
Ronaldo, 31, ruptured the main tendon in his left knee - a very serious injury that until the 1970s inevitably spelled the end of players' careers.
The Brazilian three-time World Player of the Year and record scorer in World Cup Finals suffered a similar injury to his other knee in 1999, while playing for Milan's cross-city rival Inter.
But doctors and club officials were optimistic that the same team that operated on him in 1999-2000, led by French surgeon Gerard Saillant, will get Ronaldo back in shape again.
''He has extraordinary physical qualities and I think he will recover his world-class status in a few months,'' said Milan Chairman Silvio Berlusconi.
Inter Chairman Massimo Moratti said: ''He has great strength of mind and body. What's more, the doctors know him and he's been down this road before''.
Milan doctor Walter Pascale pointed out that the Paris operation in 2000 had been ''excellent''.
He added: ''Over the past eight years surgical techniques have improved considerably''.
''If things go as they should he will recover his ability as a great player. However, it is hard to say how long it will take him to recover''.
The Italian press predicted that the injury would keep the Brazil great out for at least nine months.
Milan coach Carlo Ancelotti said: ''I don't want to say it's the end of his career because only time will tell - all we can do is stand by him''.
Ancelotti said the whole club was worried about the Brazilian, who has been dogged by injuries since joining Milan from Real Madrid last summer.
The knee injury came shortly after Ronaldo replaced Alberto Gilardino in the second half.
The Brazilian fell awkwardly while challenging for a ball in the air with Jose Vidigal,
''I heard a horrible sound, like a bang, it was a strange sound,'' said Livorno goalkeeper Marco Amelia, who was close by when Ronaldo fell to the ground.
Despite his nagging injuries, Ronaldo has scored nine goals in 16 matches for Milan.
The injury on Ronaldo's other knee occurred in November 1999. Saillant repaired the break.
But Ronaldo only lasted seven minutes on his comeback against Lazio in April 2000 before the tendon snapped again.
After more thorough reconstructive surgery in Paris, he was out for another 20 months.
Returning for Inter late in the 2001-2002 season, he was soon his old self again and scored twice against Germany in the 2002 World Cup Final as Brazil became world champions for a record fifth time.
