Kaka admits he hasn't lived up to expectations in his first season at Real Madrid.
With Madrid still locked in a tight battle with Barcelona for the Primera Division crown, the Brazilian playmaker has conceded he could have played better this season, but blamed injuries for his failure to settle into the side.
"I'm not happy with my performance, but my problem is physical," he said. "I have suffered a lot since I arrived."
Kaka has just returned from six weeks out, with his appearance - and goal - against Real Zaragoza at the weekend his first since the Champions League defeat to Lyon in March.
Kaka denied sustaining his troublesome thigh problem in that match, saying it happened in training subsequently.
"I was not hurt in the game," he said. "It was the following Saturday when I hit the ball I felt pain."