Reports have circulated in the Spanish media this week that the Portugal star has been playing through the pain of a knee injury sustained in the Champions League last-16 win over Schalke.
While Ancelotti admits he would be willing to rest the 29-year-old should any physical discomfort become serious, the Italian insists his star man will be in action this weekend.
"Cristiano has been training normally, I don't think it's been affecting his game and he will play tomorrow. It's no problem," he told a press conference. "We thought of resting him, but the problem has been managed well and he is confident. If things don't improve, we'll give him a break. It's a small problem."
Ancelotti also said he would not drop Diego Lopez in favour of Iker Casillas for Saturday's clash despite some calls for the Spain skipper to be returned to the full-time No.1 role following Lopez's showing in the defeat to Sevilla.
"It's something I've already spoken about. Things can change, but Diego Lopez has been doing well, like Iker. Diego Lopez will play tomorrow, Iker on Wednesday," Ancelotti said.
The former Paris Saint-Germain coach also claimed Xabi Alonso does not need to be rested despite two disappointing showings in Madrid's back-to-back defeats.
"The last two games haven't been great, but the player is physically fine. It may be that he has made mistakes but he is a very important player," he said. "When he needs rest, he will rest. In the two defeats the team showed a good physical condition."
Madrid will be desperate to return to winning ways after seeing its lead at the top of La Liga disappear in the last two matchdays and Ancelotti has called for a greater level of concentration from his side.
"It's not just a problem in our play. We've conceded six goals and we need to avoid these kind of errors because we paid dearly for them," he added. "We need more concentration than normal."