(CNN) -- Three-time FIFA world player of the year Ronaldo announced his retirement from football on Monday in an emotional press conference which brought an end to his 18-year career.
The 34-year-old former Brazil striker, who in 2006 became the all-time leading scorer at the World Cup, cited injury and a lack of fitness as the reasons behind his decision to end his contract with Sao Paulo-based club Corinthians.
"As you can imagine and you heard during the whole weekend, I'm here to (confirm that) I'm closing my career as a professional player," the former Barcelona, Inter Milan and Real Madrid star told reporters at a press conference.
Ronaldo, who has struggled with his weight in recent years, also revealed that he has hypothyroidism -- an illness which affects the body's metabolism.
"Four years ago at Milan I discovered I was suffering from a complaint called hypothyroidism, which slows down your metabolism, and to control it I would have to take some hormones that are not permitted in football because of anti-doping (rules)," he said.
"The pain made me anticipate the end of my career. My career was beautiful, was wonderful. I've had many defeats but infinite victories."
Ronaldo has won the World Cup twice, in 1994 and 2002, and his 15 goals in football's premier tournament is a record.
The two-time Copa America winner played for some of football's most-famous clubs, and also had spells at PSV Eindhoven and AC Milan during his 13 years in Europe.
"It's very hard to leave something that made me so happy. Mentally, I wanted to continue, but I have to acknowledge that I lost (the fight) to my body," a visibly upset Ronaldo said.
Ronaldo won the now-defunct European Cup Winners' Cup with Barca in 1997 and the 1998 UEFA Cup with Inter, scoring in the final of both competitions.
"Il Fenomeno" -- as he was dubbed after his time with Inter -- went on to win two Spanish first division titles with Real in 2003 and 2007.
But Ronaldo has suffered criticism from Corinthians fans following the club's recent elimination from the Copa Libertadores by Colombia's Deportes Tolima.
The supporters' anger led to the players' cars being vandalized and "Ronaldo is a shameless fatty" being painted on a wall at the club's training ground.
But the veteran forward showed no ill-feeling towards the fans, and instead praised their enthusiasm.
"I've never seen fans with so much passion," said Ronaldo, who was a boyhood supporter of Rio de Janeiro club Fluminense.
Ronaldo's footballing achievements have at times been overshadowed by controversy, starting with his late withdrawal and then reinstatement before the 1998 World Cup final against France -- which Brazil lost 3-0.
He has had several high-profile relationships, and after a parental test last year showed he had fathered his fourth child to a waitress he met in 2002, Ronaldo announced he'd had a vasectomy.
He hit the headlines for the wrong reasons in 2008 when he admitted picking up three prostitutes who turned out to be transvestites. Ronaldo accused one of them of trying to extort money from him.
But despite his recent problems, he will be remembered as one of the greats of the game.
Meanwhile, Roberto Carlos -- who played alongside Ronaldo for Real, Brazil and most recently Corinthians -- has also ended his stay in Sao Paulo and joined Russian team Anzhi Makhachkala.
The 37-year-old, who was also a World Cup winner in 2002, had been with Corinthians since he left Turkish side Fenerbahce in 2010.
The full-back is most famous for his 11-season stay in Madrid, where he won the European Champions League three times between 1998 and 2002.