Sir Alex Ferguson poses with new signings Kleberson and Cristiano Ronaldo at Old Trafford in 2003. Getty Images
Cristiano Ronaldo and his Manchester United teammates celebrate with the Champions League trophy after defeating Chelsea in the final in 2008 in Moscow. They won in a penalty shootout after a 1-1 draw. Ronaldo made his way back to Old Trafford after leaving Juventus. Getty Images
Cristiano Ronaldo is crowned the European Footballer of the Year in 2008, flanked by previous winners and former Manchester United players Denis Law (L) and Bobby Charlton. Getty Images
Cristiano Ronaldo lifts the FIFA Club World Cup in 2008 after Manchester United defeated Liga De Quito of Ecuador 1-0. Getty Images
Ronaldo savours the sweet taste of victory after Manchester United's 2008 Champions League win. Getty Images
Ronaldo soared above the Chelsea defence to net before Frank Lampard equalised shortly before half-time. Getty Images
Ronaldo celebrates after scoring the opening goal of the 2008 UEFA Champions League Final. Getty Images
Cristiano Ronaldo lifts the Premier League trophy with his Manchester United teammates in 2008. Getty Images
Ex-Man United manager Sir Alex Ferguson and Cristiano Ronaldo compare skills during a training session in 2008. But will the Portuguese return to Old Trafford? Getty Images
Ronaldo holds off the challenge of Lionel Messi during the Champions League semi-final against Barcelona in 2008. Getty Images
(L-R) Louis Saha, Wayne Rooney and Cristiano Ronaldo pose with the League Cup trophy after defeating Wigan Athletic in 2006. Getty Images
Rio Ferdinand congratulates goal scorer Cristiano Ronaldo during a Premier League match in 2005. Getty Images
Cristiano Ronaldo makes his debut for Manchester United in August 2003. Getty Images
A Manchester United fan wears the shirt of new signing Cristiano Ronaldo outside Old Trafford in 2003. Getty Images
Sir Alex Ferguson poses with new signings Kleberson and Cristiano Ronaldo at Old Trafford in 2003. Getty Images
Cristiano Ronaldo and his Manchester United teammates celebrate with the Champions League trophy after defeating Chelsea in the final in 2008 in Moscow. They won in a penalty shootout after a 1-1 draw. Ronaldo made his way back to Old Trafford after leaving Juventus. Getty Images
Cristiano Ronaldo is crowned the European Footballer of the Year in 2008, flanked by previous winners and former Manchester United players Denis Law (L) and Bobby Charlton. Getty Images
Cristiano Ronaldo lifts the FIFA Club World Cup in 2008 after Manchester United defeated Liga De Quito of Ecuador 1-0. Getty Images
Ronaldo savours the sweet taste of victory after Manchester United's 2008 Champions League win. Getty Images
Ronaldo soared above the Chelsea defence to net before Frank Lampard equalised shortly before half-time. Getty Images
Ronaldo celebrates after scoring the opening goal of the 2008 UEFA Champions League Final. Getty Images
Cristiano Ronaldo lifts the Premier League trophy with his Manchester United teammates in 2008. Getty Images
Ex-Man United manager Sir Alex Ferguson and Cristiano Ronaldo compare skills during a training session in 2008. But will the Portuguese return to Old Trafford? Getty Images
Ronaldo holds off the challenge of Lionel Messi during the Champions League semi-final against Barcelona in 2008. Getty Images
(L-R) Louis Saha, Wayne Rooney and Cristiano Ronaldo pose with the League Cup trophy after defeating Wigan Athletic in 2006. Getty Images
Rio Ferdinand congratulates goal scorer Cristiano Ronaldo during a Premier League match in 2005. Getty Images
Cristiano Ronaldo makes his debut for Manchester United in August 2003. Getty Images
A Manchester United fan wears the shirt of new signing Cristiano Ronaldo outside Old Trafford in 2003. Getty Images
Sir Alex Ferguson poses with new signings Kleberson and Cristiano Ronaldo at Old Trafford in 2003. Getty Images