Khedira looks set to miss the rest of the season after tearing the anterior cruciate ligament in his right knee during Germany's friendly with Italy on Friday night.
That is a major blow for both Germany and Madrid, where Khedira has been a regular starter under Ancelotti and also his predecessor Jose Mourinho.
However, the Spanish giants are unlikely to try and seek cover for the 26-year-old, with Ancelotti pointing out the likes of Isco and Casemiro are capable of stepping in.
Ancelotti said in Madrid at the launch for his book: "We don't have any plans to sign anyone during the winter transfer window.
"We have two options. One is to use a player with a similar style and the other is to change our system.
"I think I need to think about this, and we have players who at the moment have not played, but are in good shape like Casemiro.
"Isco has played some matches in the middle of a three-man midfield, although he is more comfortable playing behind the forwards.
"I might be able to go with two midfielders and Isco a little further forward. Pepe and (Sergio) Ramos are central defenders."