Madrid Goalkeeper is believed to have suffered the injury to his left knee in training.
The Belgium international is believed to have injured the anterior cruciate ligament in his left knee in training and will undergo surgery in the coming days.
A statement on Real’s official club website read: “Following tests carried out on Thibaut Courtois, the player has been diagnosed with a torn anterior cruciate ligament in his left knee. The player will undergo surgery in the coming days.”
The 31-year-old has made over 200 appearances for the club since joining from Chelsea in August 2018 and is a near-ubiquitous presence in the Spanish capital.
Courtois’ best performance came in the 2022 UEFA Champions League final as Los Blancos beat Liverpool 1-0 in Paris.
Spain international David De Gea, who was previously linked with a big move to the Santiago Bernabeu, could be an alternative for Carlo Ancelotti after his contract at Manchester United expired this summer.