Real Madrid midfielder Kaka (R) from Brazil leaves the Apra AZ Monica Clinic after an operation on his left knee in Antwerp August 6, 2010. Kaka has been operated by Belgian doctor Marc Martens, specialized in sport injury, and could be ruled out for three to four months, the clinic which carried out the surgery said on Thursday. [Xinhua/Reuters Photo]

Real Madrid's Brazilian midfielder has defended himself over accusations that he pushed himself too hard during the World Cup causing the knee injury that will keep him out of action for up to four months.

The midfielder flew to Belgium from Real Madrid's Los Angeles training camp on Wednesday and on Thursday he underwent an operation on a torn meniscus ligament in his left knee.

He will now be out of action until at least November, prompting criticism that the injury was caused by him working too hard in the World Cup finals, after last season saw him struggle with a pelvic injury.

Speaking in Saturday's edition of sports paper Diario AS, Kaka admitted that the knee had been troubling him for a while, but insisted that the club knew all about him problem.

"The knee had been causing me problems for a while, but I didn' t know it was so important," he said.

"It began to hurt before the World Cup and I always made it clear that it gave me a few problems in Madrid, but I was always having treatment on my pelvic problem and it seemed as if it was just a muscle imbalance that would not be as serious as it is now."

"I told the doctors about it various times, they knew all about it, but we all thought it was a problem that was related to the pelvic injury. That is why it was not wrong for me to play in the World Cup," he insisted.

Kaka only completed 90 minutes on 12 occasions last season and after Real Madrid had spent 65 million euros (84 million dollars) in signing him from AC Milan that has to be seen as a disappointment.

All the player wants to do now is recover in order to be able to show his true worth.

"This is a nightmare, but I am going to do all I can to get fit so that I can win titles in this Real Madrid. I am the first person who wants to see me fully fit," he said.