Karim Benzema is set for a spell on the sidelines after Real Madrid confirmed the striker sustained an injury to his right hamstring in their derby defeat to Atletico.
Benzema was withdrawn at half-time on Saturday and reports in Spain suggest he could be out for between three and four weeks.
If that is the case, Benzema will miss La Liga matches against Levante, Celta Vigo, Las Palmas and Sevilla, as well as the Champions League last-16 second-leg tie against Roma.
Benzema is now also facing a race against time to recover in time to face fierce rivals Barcelona in the Clasico on April 2 at Camp Nou.
A Real Madrid statement read: "After tests, Karim Benzema has been diagnosed with a muscle injury to his right hamstring."
Benzema returned to the fold to face Atletico having missed Real's previous Liga fixture against Malaga with a hip injury.
The former Lyon star has scored 19 La Liga goals this season, a return bettered only by Barca star Luis Suarez and Madrid team-mate Cristiano Ronaldo.
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