Real Madrid striker Kylian Mbappe is a doubt for the Clasico on 10 May after his club confirmed on Monday he has sustained a thigh injury.
"He has been diagnosed with an injury to the semitendinosus muscle in his left leg," said Los Blancos in a statement, after the France captain went off hurt during Madrid's 1-1 draw against Real Betis in LaLiga last Friday.
Madrid, second in the Spanish top flight by 11 points from leaders Barcelona, face Espanyol on Sunday before taking on the Catalan giants the following weekend.
Real Madrid initially indicated Mbappe had suffered a muscular overload, but further tests showed their top goalscorer was injured.
If Madrid drop points against Espanyol without him and Barcelona defeat Osasuna on Saturday, Hansi Flick's side will be crowned champions for a second successive season.
Mbappe has been troubled by injury this season, generating concern in France with the World Cup in the United States, Canada and Mexico starting on 11 June.
The 27-year-old, a world champion in 2018, was dogged by a knee issue which lasted for two months, the longest absence of his career, and admitted it caused him "frustration, anger and anxiety".