The Portuguese is facing a domestic ban after seeing red in the 1-1 draw with Athletic Bilbao at the weekend, but will take part in the contest at the Bernabeu.
"Ronaldo will start tomorrow. His red card was a harsh decision. Cristiano gets provoked a lot and receives many tackles in every game," Ancelotti told reporters at a press conference.
"[Fabio] Coentrao and [Alvaro] Arbeloa will both play tomorrow. [Gareth] Bale is available to play. He trained well.
"[Raphael] Varane is fine. If he doesn't play tomorrow, he will play on Saturday."
Madrid lost in the final of the Copa del Rey to Atletico last season.