The Italian, whose side host Elche this weekend, has followed a strict selection policy as regards to his goalkeepers this season, with Casillas playing every Copa del Rey and Champions League game, and Diego Lopez turning out for every league match.
In an informal chat with journalists, Ancelotti was asked what he would do if Madrid qualified for the Champions League final, given Casillas would not have played since the Copa del Rey final a month earlier.
He said: "I'm not ruling out fielding Iker in one or two league games, we will discuss that if we do make the Champions League final".
Real go into the game at the Estadio Santiago Bernabeu unbeaten in 25 games, equal with their second-best mark set in the 1996-97 season. Their all-time unbeaten streak in competitive matches is 34, set in the 1988-89 campaign.
Elche goalkeeper Manu Herrera insists his team are looking forward to their trip to the Bernabeu, while at the same time acknowledging they will have to play a "perfect" game if they are to pick up a positive result.
"We have a great week ahead of us because we are playing Real Madrid at the Bernabeu, a stage everyone wants to compete on and we are very keen to perform well there," he told reporters.
"We go there with the hope of winning, of going there and competing and making things difficult for Real Madrid. We're going to try and complicate the game for them and make our presence felt."
But he added: "We will have to have a perfect game."