Real Madrid captain Dani Carvajal is set to undergo keyhole surgery on his right knee.
The 33-year-old Spain defender underwent tests on Monday morning after feeling discomfort following his arrival as a 72nd-minute substitute in Madrid's 2-1 El Clasico victory over Barcelona on Sunday.
A club statement read: "Following tests carried out on our captain, Dani Carvajal, by the Real Madrid Medical Services, he has been diagnosed with a loose joint in his right knee.
"Carvajal will undergo arthroscopy."
Carvajal's appearance in El Clasico was his first since suffering a calf injury in Los Blancos' 5-2 defeat to city rivals Atletico Madrid on September 27.
Madrid did not specify in the statement how long Carvajal would be out, but sources told ESPN that the LaLiga leaders hope to have him back at the start of 2026.
Information from PA was used in this report.