MADRID (Reuters) -- Real Madrid and Brazil playmaker Kaka, the 2007 World Player of the Year, will be out for about 15 days after injuring the left knee that was operated on following the 2010 World Cup.

Kaka, who made his first appearance of the season for the Spanish club in January, had a series of tests which revealed the extent of the knee problem, the team said on their website (www.realmadrid.com) on Tuesday.

The 28-year-old former AC Milan player will miss Saturday's La Liga match at home to Hercules as well as next week's Champions League last-16 second leg against Olympique Lyon, also at Real's Bernabeu stadium.

Coach Jose Mourinho told a news conference on Saturday it was better for Kaka, who has struggled to regain his best form since his return, to get properly fit before playing again.

SI Apps
We've Got Apps Too
Get expert analysis, unrivaled access, and the award-winning storytelling only SI can provide - from Peter King, Tom Verducci, Lee Jenkins, Seth Davis, and more - delivered straight to you, along with up-to-the-minute news and live scores.