Casillas is yet to feature in La Liga under Ancelotti, instead being selected for Copa del Rey and UEFA Champions League fixtures, while Lopez is an ever-present in this season's Spanish top flight.
With the final of the Copa del Rey against Barcelona approaching, Ancelotti will have a decision to make on whether to stick with Casillas or bring in Lopez for the showpiece in April.
However, the Italian is pleased with both his goalkeepers and played down comparisons to a similar situation he encountered at Italian giants Milan with Christian Abbiati and Dida.
"At Milan I rotated the goalies because of the injury to Abbiati," he said. "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."
Ancelotti's defensive ranks have been boosted recently with the return to action of France international Raphael Varane.
Having played the full match against Atletico Madrid in the Copa del Rey on Tuesday after a knee problem - his first start since November - Ancelotti confirmed that the 20-year-old came through the game without any problems and could now come into contention to face Getafe on Sunday.
"Varane's knee responded well last Tuesday. He will be in the squad (for Sunday's game)," Ancelotti added.
"I don't think he is going to play from the beginning but he is available."
