The Spanish goalkeeper came under criticism for his performances at the World Cup this summer, but Ancelotti has insisted that he has "complete confidence" in the long-serving stopper.
"Iker will play tomorrow, he's fine and deserves to play. He did well in the Champions League last season," he told reporters at a press conference.
"Iker is a great goalkeeper and had a great season last year. He will do great this year too. Everyone makes mistakes in a game. Including myself in regards to the line-ups. It's normal in this world to make mistakes. I have complete confidence in Iker."
New signing Keylor Navas will start on the bench for Madrid tonight.