Bale began his career at left-back at Southampton and Tottenham Hotspur before twice becoming Premier League Player of the Year from a more advanced position and Ancelotti insisted that the Welshman would maintain his place on the right side of Real's attack.
"Bale at full-back is not an option for us," he told reporters ahead of Dortmund's visit to the Spanish capital. "We have a problem with Marcelo, but we can cover his absence well with (Fabio) Coentrao. He is fresh and will replace him without any problems."
Bale was on target twice in Real's 5-0 win over Rayo Vallecano on Saturday as Ancelotti's men bounced back from consecutive defeats to Barcelona and Sevilla.
Ancelotti admitted that Bale can be inconsistent, but defended the player's attitude and claimed that was to be expected given the type of player he is and the position he plays in.
"I think it is true he is a little intermittent, but that is a characteristic of all forwards and especially very quick players."