Ronaldinho suffered a significant dip in form throughout the past three years after he was named FIFA Footballer of the Year in 2004 and 2005.

"I don't know what happened to Ronaldinho but it has been three years without any change," Kaka told a press conference.

"He needs to find the motivation to go back to being one of the best players in the world."

Kaka will face his former AC Milan mate as the Rossoneri clash with Real on Wednesday.