Van Nistelrooy was forced off in the final 10 minutes of Madrid's Champions League defeat to Juventus on Wednesday.

And initial tests suggest the injury is worse than first feared, with the Dutchman now set to visit knee surgeon Dr Richard Steadman.

"The worst injury news concerns Ruud van Nistelrooy," said a statement on the official club website, www.realmadrid.com.

"Following clinical exploration and MRI scans this Friday, Real Madrid's medical team have detected a possible tear in the external cartilage of the right knee, operated on in 2000 by Dr Steadman.

"They will consult the aforementioned doctor to evaluate the different ways to cure this tear."

The problem is related to an old injury which forced Van Nistelrooy to undergo surgery in Holland last spring.

The 32-year-old is the latest Madrid player facing a lengthy lay-off after it was revealed Arjen Robben will be out of action for up to six weeks, while Ruben de la Red is also out indefinitely.