The Spanish club said earlier on their website that Kaka had suspected meniscus damage and might need surgery.

He was examined by knee and sports injury specialist Marc Martens in Belgium and Martens's assistant at the clinic in Antwerp told Reuters that a half-hour arthroscopic operation was carried out on Thursday morning.

"It went well," the assistant said. "The typical recovery period for this is three to four months." Brazilian Kaka, who has been plagued by injuries over the past year but recovered to play in the World Cup in South Africa, had left Real's pre-season training camp in California to fly to Belgium.

"He's a very popular player among his team mates and also a very good player but we want him at 100 percent so that he is happy," coach Jose Mourinho told a news conference in San Francisco after Real beat Club America 3-2 in a friendly.

"If we have to lose him for a while it won't be a drama," the Portuguese added. "We have other players and that's that." Kaka, 28, joined Real from AC Milan in 2009 for a fee of around 65 million euros ($85.3 million). He made 25 league appearances last season, scoring eight goals.

Real play a friendly against Major League Soccer (MLS) club LA Galaxy on Saturday in Los Angeles.
 
Chelsea poised to sign Ramires

Meantime, Chelsea have agreed to sign Brazil midfielder Ramires from Benfica for a fee of 22 million euros ($29.10 million), the Portuguese club said on Wednesday.

The deal is subject to the 23 year-old passing a medical at the English Premier League club.

Ramires joined Benfica from Cruzeiro in May 2009 and a month later he earned his first senior cap for Brazil.

He played a key part in the Benfica team which lifted the Portuguese title in May for the first time in five years, making 26 appearances and scoring four goals.

The pacy versatile midfielder went on to earn another 15 caps, including five appearances at the Confederations Cup in 2009 and four at this year's World Cup in South Africa, where Brazil were knocked out by the Netherlands in the quarterfinals.