The Dutch forward travelled to the United States this week to see leading specialist Dr Richard Steadman about his injured right knee, and yesterday underwent an exploratory arthroscopic operation to determine the extent of the problem.

Van Nistelrooy suffered the injury during last week's 2-0 defeat against Juventus in the Champions League.

The former Holland international had hoped to be absent for only a couple of months, but the results of those tests revealed the damage was more serious than first thought and Madrid confirmed yesterday that he could be out until August.

That leaves Schuster with Raul, the in-form Gonzalo Higuain, and Javier Saviola as his only attacking options.

Following meetings with the squad and club president Ramon Calderon, Schuster announced this afternoon the injury to Van Nistelrooy has convinced the club to explore their options ahead of the coming transfer period.

"We're trying to see if there are any possibilities. If there are, we'll take them for sure," Schuster told Spanish newspaper Marca.

"Ruud's lay-off doesn't mean we have to sign someone, but it does mean we have to be more aware of what's happening in the market because we'll be a man down for a long time.

"Although it's not great having this obligation to sign someone, which we didn't have before, we'll see if we can be lucky and if someone important can come and help us."

Reports in Spain suggest Inter Milan's Hernan Crespo is seen by the Spanish champions as an ideal short-term solution.