The Portuguese forward was substituted in the early stages of his side's 1-1 draw with Real Valladolid on Wednesday with a suspected thigh problem.
And in his pre-match press conference on Saturday, Ancelotti revealed his talisman will sit out the game at Vigo, with a UEFA Champions League final with Atletico Madrid still to come on May 24.
"Cristiano won't play because he isn't at 100 per cent," he said.
"We are not thinking about the final. If we were to play it tomorrow, we would risk it with him.
"I've always said we won't risk it because Cristiano isn't at his 100 per cent. We have to win without him."
Ancelotti also confirmed that Sami Khedira could feature for the first time since damaging knee ligaments for Germany back in November.
The midfielder has been an unused substitute in each of Real's last two matches and Ancelotti says Khedira is raring to go.
"Khedira is fine," he said.
"He hasn't had any problems and can't wait to play.
"(Alvaro) Arbeloa and Khedira have both worked very hard. It's incredible."
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