The Portugal forward has not featured for Real since their 3-0 UEFA Champions League quarter-final first-leg win over Borussia Dortmund on April 2 because of a knee complaint.
Ronaldo was left on the bench for the second leg of that tie as Real scraped through 3-2 on aggregate following a 2-0 loss at Signal Iduna Park.
However, the capital club have since revealed that the 29-year-old also has "an injury to the left biceps' femoris muscle" in his thigh.
The former Manchester United man was unavailable for Saturday's 4-0 La Liga win over Almeria, and will again be on the sidelines as Real look to repeat what they achieved in 2011 by beating arch rivals Barca in the Copa final.
"Ronaldo will not be there, we know that since this morning (Tuesday)," Ancelotti said. "But the team has always reacted well to absences and will again tomorrow."
However, the Italian insisted that Real will not alter their approach to compensate for Ronaldo's absence.
"Cristiano is not available to play because we do not want to take risks as we have other important games this season," he added.
"Cristiano's absence makes everyone more motivated. We have played very well in games he's missed, worked more, ran more.
"Our plan will not change. It's the same with or without Cristiano. We have to consider the quality of our rivals."
