A recent hamstring injury reportedly meant that the Portuguese would miss the next two weeks of the season.
However, Ancelotti has claimed that his leading scorer could be fit for the clash at the Mestalla.
"He's making progress every day and I'm not ruling him out, but we won't run any risks with him," he told El Mundo.
"There will be no change of system if he can't play. The players are feeling assured and comfortable. They have faith."
Ronaldo has scored 45 times in all competitions this season.