Athletic Bilbao will be without the services of striker Aritz Aduriz for four weeks.
The in-form hit-man strained knee ligaments in last weekend's goalless draw at Alaves.
Aduriz - who joined in the January transfer window from Real Valladolid - sustained the injury after colliding with Alaves keeper Franco Costanzo.
Although tests have ruled out serious damage, the 25-year-old must now spend the best part of a month on the sidelines at a time when his team need him most.
The Basque outfit are battling to avoid relegation and the goals of Aduriz have proved crucial over the past few weeks.
He has bagged seven since his January move and helped move Athletic out of the drop-zone.
He will now spend a week resting before beginning his recovery programme.