Real Madrid have announced Kaka has undergone successful surgery on a long-standing knee injury but he will face up to four months on the sidelines.
Kaka saw a Belgian knee specialist on Thursday after leaving Real's tour of America, which got underway on Wednesday with a 3-2 pre-season friendly win over Mexico's Club America.
A statement on Real Madrid's website read: "The operation performed on the left knee of Real Madrid C.F.'s Ricardo Izecson Dos Santos Leite 'Kaka' by Dr. Marc Martens at Antwerp's AZ Monica Hospital was a success.
"The arthroscopic surgery confirmed an injury to the left meniscus with minimal inflammation of the cartilage. The player is expected to miss three to four months."
Jose Mourinho is confident Madrid can cope in the absence of Kaka. He said: "If we lose him for some time it's no drama, we have other players and that's it, but he's one of the best players in the world."
Kaka failed to impress at this summer's World Cup as Brazil's campaign ended in the quarter-finals. As well as receiving a red card against Ivory Coast he was hampered by a groin injury, which also derailed his first season at the Bernabeu, though Real's club statement said that this injury had improved.