Cristiano Ronaldo's pursuit of perfection is what makes him a world-class footballer, according to his former Portugal teammate Deco.
Former Barcelona playmaker Deco played alongside Real Madrid's Ronaldo, 30, at international level for the Seleccao.
Deco was taken aback by Ronaldo's work ethic in training, something which has helped him win numerous trophies including three separate Ballon d'Or awards.
"The guy isn't well in the head, I've never seen anyone train like it, it's not easy to be like that," Deco told ESPN, as quoted by AS.
Having also played with Lionel Messi at Barca, Deco compared the two superstars, adding: "They're completely different.
"Messi looks after his body as an athlete should, but what Cristiano does is incredible. He goes to insane lengths because he always wants to be the best in every way and he competes to win everything.
"It's amazing to see both players in action, but impossible to make a comparison."