Cristiano Ronaldo has revealed the toughest opponent he has ever faced is former Arsenal and Chelsea defender Ashley Cole.
The duo met on several occasions during Ronaldo's six-year spell with Manchester United and also while on international duty with Portugal and England.
And although Ronaldo has since tested himself against numerous defenders in La Liga, the Champions League and on the international stage, he still rates Cole highly.
"Over the years I had some great battles with Ashley Cole, he does not give you a second to breathe," Ronaldo told Coach Mag. "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 was also questioned about the player he admired most - even if he admitted they weren't "good friends".
"There is a big mutual respect between myself and Lionel Messi," Ronaldo added. "The media like to make out like we have this big rivalry, but we don't.
"It is not like we are good friends, but there is a mutual respect on both sides."
As well as respect for Messi, the Real Madrid star revealed his admiration for former Manchester United manager Sir Alex Ferguson.
"I do see Sir Alex Ferguson as a father figure," Ronaldo said. "All my coaches have been important, but when I arrived at Real Madrid I was a man, when I arrived at Manchester United I was a boy.
"All of a sudden you are at one of the biggest clubs in the world, and at that time I needed somebody like Sir Alex."