The striker underwent surgery in 2000 before joining Manchester United from PSV Eindhoven.

The Dutchman flew to America to consult leading surgeon Richard Steadman, who had previously operated on him, and looks set to be sidelined for six to nine months.

"Following an exploratory arthroscopic operation on Wednesday, it was determined that Ruud van Nistelrooy had a partially torn meniscus in his right knee," Real Madrid stated on their official 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."

The 32-year-old aggravated the injury in October in their UEFA Champions League match against Juventus. Real could now be forced to bring in reinforcements up front in January.

(Source: Soccer365.com)