The extent of the injury should be known later today...
Dutch striker van Nistelrooy scored Madrid's final goal in the 5-0 rout of the Primera Division newcomers at the Bernebeu but according to reports in the Spanish press he has possibly suffered a torn thigh muscle in his left leg.
Madrid lead thanks to an early strike from Cristiano Ronaldo before a flurry of late goals in the final fifteen minutes completed the comprehensive win for Los Merengues.
The 33-year-old was introduced as an 80th minute substitute for Ronaldo and scored with just a couple for minutes remaining on the clock. It was van Nistelrooy's first goal for Madrid since scoring for the Blancos against Juventus in the UEFA Champions League last October.
He had only recently completed a comeback after knee surgery last year which ruled him out of football for almost nine months.
Paul Madden, Goal.com