The Blancos forward has been out of action since late November with a thigh injury picked up against Almeria which prevented him from playing in a Liga clash against Valladolid and a European tie at home to Galatasaray.
The Portuguese attacker is suspended for Saturday's Copa del Rey trip to third-tier Olimpic de Xativa but Ancelotti has revealed that Ronaldo is back training and likely to feature at Parken.
"Cristiano is fine," Ancelotti told reporters. "He trained well and will play [in the Champions League] on Tuesday.
"Xabi Alonso won't play tomorrow [Saturday] because playing on an artificial pitch is not good for his injury.
"We have trained well this week. We have no problems to use a strong side [on Saturday]."
Alonso has been repeatedly linked with a move away from Madrid of late but Ancelotti is not unduly worried by the speculation surrounding the former Liverpool playmaker.
"Xabi Alonso will decide his own future," the Italian added. "He is calm and I speak with him a lot."
Ancelotti spoke of his delight at the progress made in recent weeks by Gareth Bale, who joined the club for a world-record fee during the summer.
"Bale is fitter and better than he was when he came," Ancelotti said. "He is very happy. Bale links up well with his team-mates. He is happy and everyone else is happy with him."