And the superstar forward revealed that he came up against his toughest opponent when he was plying his trade in England's top flight.
Speaking to Coach Mag, the Portuguese international hailed the former Arsenal and Chelsea defender while calling him his toughest opponent.
"Over the years I had some great battles with Ashley Cole," he said. "He does not give you a second to breathe.
"He was such a tenacious player when he was at his peak, quick, tough in the tackle. You knew it would never be an easy game."
Ronaldo and Cole met on several occasions in the Premier League and on international duty.
But the former left-back failed to return the compliment when he was asked to pick between Ronaldo and Lionel Messi.
He didn't hesitate, immediately siding with the Barcelona man.
"It has to be Messi," he said.
Cole admitted Messi "was just too good" for him while adding a playful comment.
"People talk about Ronaldo more because I played against him more. But I think to mark Messi, on his day... he was just too good for me.
"But, again, he's never scored [against me]," he added.