AC Milan coach Massimiliano Allegri hailed Kaka's performance after their 1-1 draw with Champions League opponents Barcelona.
The Brazil international was superb on the night, setting up Robinho's goal.
"Kaka had an extraordinary game and he proved he is a champion. I don't mean just in technical terms, as we all know that, but he worked so hard and even acted as a full-back at times when harassing the Barcelona players.
"Kaka proved once again to be a champion it's not enough to have great feet, but to work hard and put the effort in," said Allegri.
