Brazil team doctor Jose Luiz Runco admitted on Sunday that star midfielder Kaka, who failed to shine at the World Cup, was not properly fit and wouldn't have played at a lesser event.

"Maybe in other situations Kaka would not have played even the World Cup, but he really wanted to be there," said Runco as the squad touched down in Rio following their flight back from South Africa.

Kaka came into the tournament on the back of a disappointing season with Real Madrid which was marred by thigh problems which forced him to miss more than six weeks of the season.

And when he did play the 65 million euro ($A96.47 million) summer signing from AC Milan did not hit the heights, prompting him to admit that he had himself not been happy.

"I suffered a lot since I got injured," the 2007 world and European footballer of the year told journalists.

Fans were not impressed and whistles and jeers were aimed in his direction during Real's defeat by Lyon in the last 16 of the Champions League in March.

But he shrugged it all off.

"They did it in Sao Paulo, Brazil, with Milan ... it happens to all players. The fans are very emotional," he said.

Kaka failed to score in the World Cup and was also red-carded, albeit unjustly, in the group win over Ivory Coast.

Brazil were eliminated by the Netherlands in the quarter-finals.

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