Ronaldo won the Ballon d'Or for the third time in January after a sensational 2014, but suffered a dip in form in the second half of the campaign as Madrid toiled domestically and in Europe.
The club will end the season trophyless, with some critics pointing the finger of blame at the 30-year-old, but Ancelotti says that would be most unfair.
"Ronaldo has reached a point where one does not know how many goals he scored," he told reporters at Friday's pre-match press conference. "I know I've lost the count.
"He has done the most for the team to win titles. Ronaldo cannot be asked more than he has done this year."
In addition to being bombarded with questions about his future from journalists amid rumours he will be replaced by Rafa Benitez, Ancelotti was also asked about what Paul Pogba would add to Madrid if they bought him from Juventus in the upcoming transfer window.
"Pogba is a great player, he's young and he's going to have a great future," the Italian added. "He would be good for Real Madrid because he would be good for all teams. He is one of the best young players in Europe right now."