Madrid - Real Madrid striker Ruud van Nistelrooy is expected to be sidelined for the rest of the season after undergoing surgery on his right knee in the United States, the club said Thursday.

The loss of the Dutch striker is a further blow to the club's embattled German coach Bernd Schuster.

Van Nistelrooy, 32, was treated by knee specialist Richard Steadman, who had already operated on the striker's right knee in 2000.

He will be out of action for between six to nine months, depending on how the knee recovers, the club said.

"Following an exploratory arthroscopic operation on Wednesday, it was determined that Ruud van Nistelrooy had a partially torn meniscus in his right knee," a statement said on the club website.

"Real Madrid's medical staff, Dr. Steadman and the player decided to surgically repair the damaged knee, by which he will miss between six and nine months."

Former Germany international Schuster is under pressure at Real following this week's exit in the Spanish cup at the hands of third- division side Real Union.

The side also suffered two defeats to Juventus in the Champions League and are lying a relatively disappointing fourth in the Primera Division.