Real Madrid striker Kylian Mbappe has sustained a thigh injury ahead of this weekend's LaLiga derby with Atletico, his club said on Wednesday.
The French superstar was taken off during the 3-2 win over Alaves on Tuesday and appeared to be suffering some discomfort.
Spanish media suggest Mbappe will miss around three weeks injured.
"Following tests carried out today by Real Madrid's medical services on our player Kylian Mbappe, he has been diagnosed with an injury to the biceps femoris in his left leg," said the Spanish champions in a statement.
Mbappe scored a superb goal in the thriller at the Santiago Bernabeu with Alaves and has netted five times this season in seven league appearances.
Asked about Mbappe's condition after the game, Real Madrid coach Carlo Ancelotti said: "He's fine, he's fine, a little overloaded, he asked me for the change to avoid problems."
Madrid, a point behind leaders Barcelona ahead of the Catalans' match on Wednesday against Getafe, visit the Metropolitano stadium on Sunday to face rivals Atletico.
Los Blancos have not been beaten in LaLiga for 39 games, since a defeat at Atletico a year ago.
The striker is also set to miss the visit to Lille in the Champions League next week and potentially October's Nations League matches against Israel and Belgium with France.
Mbappe joined Real Madrid this summer at the end of his Paris Saint-Germain contract, fulfilling a long-held dream.
The 25-year-old hit his stride in recent matches after taking a few games to find his footing in the Spanish capital.
Mbappe has seven goals in nine appearances for Real Madrid across all competitions, scoring in the Uefa Super Cup victory over Atalanta in August and on his Champions League debut.