The Brazilian international will miss both legs of Madrid's Champions League quarter-final against Borussia Dortmund.
Bale began his career at left-back at Southampton and Tottenham before making his mark by playing in an advanced position.
Rumours have been circulation Bale would drop back Dortmund's visit to the Santiago Bernabeu on Wednesday night, but Ancelotti insists he plans to use Fabio Coentrao in the role.
"Bale at full-back is not an option for us," Ancelotti said.
"We have a problem with Marcelo, but we can cover his absence well with 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.
That double took the Wales international's tally for the season to 16, but he has been criticised for his lack of impact in Real's biggest games.
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.
"Players with that speed can't have a continuous influence likes other players with different characteristics like Xabi Alonso.
"His inconsistency is a physical characteristic of the player, like Cristiano (Ronaldo) or (Karim) Benzema. It is not an attitude problem."