The Portuguese coach has defended his compatriot against recent negative comments, and has stressed that the attacker remains a very important figure for the capital club
The Portugal international has been on the receiving end of negative comments in the past few weeks for his alleged inability to shine in the big games, but Mourinho had nothing but praise for his star player on Tuesday.
"If someone criticises Cristiano Ronaldo, he has a problem with me. We won the Copa del Rey because of his goal, and he's scored I don't know how many goals for us. He's scored countless hat-tricks, he carries so much pressure on his back," Mourinho told reporters at Tuesday's pre-match press conference in Madrid.
"But do you know which game of his I've liked best?" he continued. "The second half he gave us against Mallorca. He worked like an animal. He won the ball back for us and ended up exhausted. I told him that it was the game of his I was most proud of.
"I told him that when he works like that there's nobody who can touch him. When he works like that he doesn't have to score all the time and be the man of the match. That was his best game for me."
Mourinho, meanwhile, has called up winger Angel Di Maria for Wednesday's match but was coy on the Argentine's fitness amid reports he will miss the Barca game through injury.
"Di Maria is not at the level we had expected of him," the Portuguese said.
In La Liga, Mourinho's men lead Barca by five points after Madrid defeated Mallorca 2-1 on Saturday and the Catalans beat Betis 4-2 on Sunday.
Asked if he watched that match, the Real coach responded: "No, I watched the Milan derby."
Wednesday's cup match at the Santiago Bernabeu kicks off at 22.00CET.