Kylian Mbappé has injured his left thigh and will likely be sidelined for an undetermined period of time, Real Madrid said on Thursday.

The club did not specify the nature of the injury nor how long Mbappé will be out, saying “his progress will be monitored.”

Madrid crosses the Spanish capital to play at Rayo Vallecano on Sunday, trailing La Liga leader Barcelona by two points.

It then travels to Qatar to play the Intercontinental Cup final on Dec. 18. Sevilla follows on Dec. 22 then a short winter break until playing at Valencia on Jan. 3.

The France captain was injured on Tuesday after scoring the opening goal in Madrid’s 3-2 win at Atalanta in the Champions League. He left the game in the first half.

Mbappé has 12 goals in 22 games since joining Madrid from Paris Saint-Germain in the offseason, but he has delivered disappointing performances against major rivals.