A knee injury could prevent German midfielder Simon Rolfes from playing at the 2010 World Cup. ((OLIVER LANG/AFP/Getty Images))

Bayer Leverkusen captain Simon Rolfes underwent another operation on his knee and is in doubt for the World Cup.

The midfielder left a fitness test for German national team players in Stuttgart and had surgery Tuesday morning to repair cartilage damage on the same right knee that was operated on in July and October.

Leverkusen said Rolfes would be out for several weeks after making two brief appearances in the last two games for the Bundesliga leaders. They were his first since the October operation after he played in the 1-0 win at Russia that qualified Germany for the World Cup.

"It's going to be difficult now [for him] to make the World Cup," said Leverkusen director of sports Rudi Voeller, adding that it was too soon to say how long Rolfes may be out but it could be months.

Rolfes's absence could create problems for Germany coach Joachim Loew in South Africa.

Another defensive midfielder, Thomas Hitzlsperger, hardly comes off the bench in Stuttgart, while Loew has told veteran Torsten Frings of Werder Bremen that he is out of the picture.