Ronaldo and Juventus are in Madrid for Wednesday's Champions League opener.
Simeone said, "It's difficult to prepare something against a player, he's an animal in front of goal.
"He has an incredible record and in any situation near the box, he's dangerous. He's not easy to control, he has it all.
"We suffer and sometimes it's our turn to win, and other times we lose, but he's an animal in front of goal."
Cristiano will travel to the Estadio Wanda Metropolitano for a second time and Simeone clearly feels that the stadium could influence the game.
"In order to play a complete game, you have to go out there with hope, although sometimes the other way around when we are doing badly," he said when asked about the atmosphere.