The Spain goalkeeper has only been used in cup matches this season, with Diego Lopez preferred for La Liga fixtures.
But in preparation for their May 24 Champions League showdown against city rivals Atletico, Casillas will be used for La Liga fixtures against Real Valladolid and Celta Vigo.
Head coach Ancelotti revealed on Saturday: "Diego Lopez will play against Valencia and Celta (Vigo), Casillas against Valladolid and Espanyol.
"Casillas needs to prepare for the Champions League final during this month."
Ancelotti's side host Valencia on Sunday and the Real coach is wary of their scorned opponents after Stephane M'Bia's stoppage-time goal sent Sevilla into the UEFA Europa League final at their expense on Thursday.
Valencia trailed 2-0 after the first leg but moved into a 3-2 aggregate lead, only to be denied by M'Bia's late goal.
"Losing a chance to play in a final like what happened to Valencia is not easy," he added.
"We have to be careful. We need to win."
