Ruud van Nistelrooy faces a new spell on the sidelines after picking up an injury in Sunday's win over Xerez.
The Dutchman came off the bench to score the final goal in the 5-0 thrashing at El Santiago Bernabeu.
It was Van Nistelrooy's first goal for Madrid since last October after recovering from a serious knee injury.
However, the former Manchester United man sustained a thigh problem in scoring and it is feared he could face a month on the sidelines with the injury.
"I got hurt while scoring. I dreamed of this return. I will have an MRI [scan] and hope it isn't anything serious," Van Nistelrooy told the club's official website .
"I worked very hard to return and everything has gone well. Let's see how my quad is holding up. We aren't happy with the way we played, but it was a good match. We can improve a lot."
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