Lopez has become the Spanish giants’ first choice goalkeeper in the league during the course of the last two seasons and has played every minute for his side in the current campaign.
However, Casillas has been the preferred choice when it comes to the Champions League, having started every game in that competition.
The Italian coach thinks it would be unfair for either keeper to have to spend the whole time on the bench as he feels they are the top two in the world at the moment.
“Iker Casillas is, like Diego Lopez, a great keeper,” Ancelotti told ABC. “We have great luck but I don’t think it’s fair that we should have two great goalkeepers and then have to leave one on the bench all season.
“I accept the selection policy means we have an irregular situation, but it is also unusual to have two great goalkeepers who are the best in the world.”
The 54-year-old also discussed Sunday’s Clasico against fierce rivals Barcelona while praising the progress of Gareth Bale, who is on a fine run of form.
“In a game like the Clasico, it is all about courage, personality and character. It is like winning the Champions League: if you do not have these virtues is impossible to win," the manager said. “The progress of Bale was a matter of time. When a player misses pre-season it is normal not to be in good physical condition and there is a risk of injury.
"It was an excellent decision to sign him.”