Real Madrid defender Alvaro Arbeloa will miss the Clasico clash with Barcelona after suffering a knee injury.
The Spain international had been training as normal with a support on his right knee, and the club were initially confident the problem was not especially serious.
However, tests have since confirmed the player has fractured his right knee cap, meaning he will not be risked in matches for the next three weeks - including the fixture with Barcelona on March 23.
Arbeloa, who has made 28 appearances in all competitions for Madrid this season, will also be forced to sit out the Champions League last-16 second leg with Schalke, as well as Liga meetings with Levante, Malaga and Sevilla.
Los Blancos currently sit one point clear of Barca at the top of La Liga after 26 games.