Guler is recovering from his latest injury setback. The summer signing from Fenerbahce is yet to make his debut.
Ancelotti said: "He is in the final phase of his recovery.
"I don't know if it will be ready by the end of the year or next year. He is very close to reaching the top. I speak to all the injured and I need a lot of time, because there are many."
He added: "He has trained well. We have two trusted goalkeepers and tomorrow I will choose. There is competition in the goal. (Andriy) Lunin has done very well when he has played and deserves to be taken into account. It might be that he is going to rotate in these games. We have four games until Christmas."