Once the undisputed number one for club and country, the Spain international now finds himself filling back-up duties at Santiago Bernabeu.
Diego Lopez is the preferred choice for La Liga fixtures, meaning Casillas must make do with outings in cup and UEFA Champions League competition.
He has hinted in the recent past that should his situation fail to improve, he may be forced to consider leaving a club that has been his home for over 20 years.
Ancelotti does not consider that to be an imminent prospect, though, with the Italian tactician of the opinion that his shot-stoppers are happy with his selection process.
Ahead of a derby date with Getafe on Sunday, he said: "At Milan I rotated the goalies because of the injury to (Christian) Abbiati.
"Dida was a good substitute and kept the position in the end.
"Here it is very different and I have explained that. I allocate minutes of play between them and I think it keeps them both motivated.
"They are doing very well and I hope they'll continue to do so."