Courtois was deemed unfit ahead of the friendly against Ivory Coast on Thursday and will miss Nations League games against England and Iceland on Sunday and Wednesday respectively.
UPDATE: @thibautcourtois will be leaving the camp after his medical check-up. He is not fit to play.— Belgian Red Devils (@BelRedDevils) October 8, 2020
According to the Spanish media, the 28-year-old has an issue with his psoas muscle but is still expected to feature for Madrid against Cadiz next weekend.
Zinedine Zidane will hope that is the case after back-up keeper Andriy Lunin tested positive for coronavirus on Tuesday.
Courtois also withdrew due to an injury problem when he was called up by Roberto Martinez during the previous round of international fixtures.