Rio Ferdinand has claimed that Cristiano Ronaldo's obsession about being the best saw him become the most influential player in the Manchester United dressing room.
After joining United as a relatively unknown teenager Ronaldo went on become one of the world's greatest players before sealing a world record transfer to Real Madrid in the summer of 2009 after six years at Old Trafford .
Former team-mate Ferdinand, who played alongside the Portuguese forward, throughout his time at the club admits that Ronaldo's mindset was the strongest he ever encountered in his career and it helped turn the now Juventus star 'from a boy to a man.'
'It takes me to someone at my club at United while they were there and it's Cristiano [Ronaldo], Ronaldo told BT sport when asked about influential players.
'About mindset, I don’t know a stronger, more determined, obsessed player that I’ve shared a changing room with.
I was fortunate to watch him go from a boy to a man over a few years and him affecting training sessions. He was absolutely obsessed winning a training session and scoring the last goal.
Despite showing flashes of brilliance, Ronaldo struggled for consistency in his first couple of seasons at the club as he developed a reputation for trying too many skills, such as stepovers, when taking on defenders down opposition flanks.
Ferdinand admitted team-mate Ruud van Nistelrooy got so fed up of his failure to provide a cross, he claimed he belonged 'in a circus', a moment the former England defender believed was a crucial turning point mentally for Ronaldo in terms of taking the focus off his skills.
'It didn't happen instantly but he was unbelievably skillful and he was there to entertain the crowd, Ferdinand added.
'He used to get snapped in training but one time, he didn't take it too well and Ruud [Van Nisterooly] was the man.
'Ronaldo had the ball wide and Ruud was making the run in the box, Ronaldo didn't pass and Ruud was frustrated. "He should be in the circus", Ruud said, and Ronaldo got upset.
'He was 18 or 19 at the time. Some kids would've gone under and lost confidence. Some would've kept doing the same but Ronaldo knew that Ruud might be right then it became all about statistics.
We used to say about George Best and Beckham being the best No 7s at the club and you could see him thinking, "how can I derail them?"'
Following Van Nistelrooy's departure in 2006, Ronaldo would go on to form a lethal partnership with Wayne Rooney which helped fire the Red Devils to three straight Premier League titles as well as the Champions League in 2008.
Having scored 118 goals in 292 games for Sir Alex Ferguson's side, Ronaldo had become established as one of the world's greatest players and it landed him an £80million move to Real Madrid.
Since then, the now 35-year-old has become one of the game's greatest ever stars and Ferdinand admits that his former team-mate left Old Trafford as the best player in the world.
'When we were going to a premiere, he was asked, "who's the best player ever?", Ronaldo said "me", he added. 'He's got an ego but he's got pride and an obsessive nature and came as a kid and left as the best player in the world.'