The 30-year-old has missed his side's last two matches against Osasuna and Shakhtar Donetsk due to a back problem, and he has also been left out of the squad for this weekend's clash with Getafe.

The issue, which is said to be related to his sciatic nerve, could also rule the stopper out of next week's Champions League contest with Shakhtar.

However, Ancelotti has said that Courtois will "certainly" be available for the game with Barcelona on October 16, which is likely to be crucial in terms of the title race this season.

"With his issue, taking the flight to Warsaw might not be the best thing for him. I think he'll certainly be there for the Clasico, but we need to have a good think about whether he should make the Champions League trip," the Real Madrid boss told reporters on Friday.

Courtois's absence has opened the door for Andriy Lunin to feature, while Lucas Canizares has been moved into the first-team squad to boost the goalkeeping options available to Ancelotti.

Dani Ceballos is also currently on the sidelines with a hamstring issue, while Karim Benzema has been rested for the game with Getafe.

"He (Benzema) has played 90 minutes in two matches in a row. He might be rested tomorrow, but he's not yet ruled out for tomorrow, so if he is fine tomorrow morning then he can play the match," said Ancelotti before the decision was made to leave him out of the squad.

"He was the key to last season's success and can be the key again. I think we'll see the same Karim as always. I'm not worried about his form."

The Real Madrid boss was also asked about Antonio Rudiger ahead of the clash with Getafe, as the 29-year-old has been rotated in and out of the side this term.

Rudiger has made 10 appearances for the La Liga outfit this term, but Eder Militao and David Alaba are still regarded as the first-choice centre-back pairing at the club.

"He knows he is very important for us. He is a world-class centre-back, just like Militao and Alaba are, and Nacho too even if he's playing less," said the Italian.

"Therefore, with these four centre-backs we're good. Sometimes one will rest, and it's Nacho who has been left out more than the others. But, even that can change in the future."

Real Madrid have another seven matches to come before the end of the month, taking on Getafe, Shakhtar, Barcelona, Elche, Sevilla, RB Leipzig and Girona.