Ronaldo picked up a knock in Madrid's 3-0 victory over Borussia Dortmund on Wednesday evening, and Ancelotti has admitted that the Portuguese attacker needs to "rest" ahead of key matches later in the campaign.
The Italian told reporters: "Tomorrow, Cristiano will rest. He is tired and has a bit of a problem.
"We prefer him to stay in Madrid, work and get ready for the next game. He has played a lot of games. We just want him to rest."
The 29-year-old has netted 45 goals in 41 appearances for Real Madrid this season.