Ronaldo's favourite childhood team was S.L. Benfica. At the age of eight, he played for team C.F. Andorinha. Ronaldo joined Sporting's youth players who trained at the Alcochete. He became the only player ever to play for Sporting's U-16, U-17, U-18, B-team, and first team, all within one season.
He was first spotted by then-Liverpool F.C. manager Gérard Houllier at sixteen, but Liverpool declined to take him on because they decided he was too young and needed some time to develop his skills. However, he came to the attention of Manchester United manager Sir Alex Ferguson in the summer of 2003, when Sporting defeated United 3–1 in the inauguration of the Estádio José Alvalade in Lisbon. Ronaldo's performance impressed the Manchester United players, who urged Ferguson to sign him.
Ronaldo became Manchester United's first-ever Portuguese player when he signed for £12.24 million after the 2002–03 season.He requested the number 28 (his number at Sporting), as he did not want the pressure of living up to the expectation linked to the number 7 shirt, which had previously been worn by players such as George Best, Bryan Robson, Eric Cantona, and David Beckham. "After I joined, the manager asked me what number I'd like. I said 28. But Ferguson said 'No, you're going to have No. 7,' and the famous shirt was an extra source of motivation. I was forced to live up to such an honour.
Despite rumours circulating in March 2007 that Real Madrid were willing to pay an unprecedented €80 million (£54 million) for Ronaldo, he signed a five-year, £120,000-a-week (£31 million total) extension with United on 13 April, making him the highest-paid player in team history. On 5 June 2008, Sky Sports reported that Ronaldo had expressed an interest in moving to Real Madrid if they offered him the same amount of money the team had allegedly promised him earlier in the year. Manchester United filed a tampering complaint with FIFA on 9 June over Madrid's alleged pursuit of Ronaldo, but FIFA declined to take any action. Speculation that a transfer would happen continued until 6 August, when Ronaldo confirmed that he would stay at Manchester for at least another year.
On 15 November 2008, Ronaldo scored his 100th and 101st goals in all competitions for Manchester United. Ronaldo had now scored against each of the other 19 teams in the Premier League at the time.
On 19 March 2008, Ronaldo captained the United for the first time in his career in a home win over Bolton, scoring both goals in the 2–0 victory
- 2 times winner of FIFPro Special Young Player of the Year awards .
- Received consecutive Barclays Player of the Month honours, becoming only the third player in Premier League history to do so after Dennis Bergkamp in 1997 and Robbie Fowler in 1996.
- He won the PFA Players' Player of the Year and PFA Young Player of the Year awards, joining Andy Gray (in 1977) as the only players to receive.
- He completed the treble by winning the PFA Fans' Player of the Year.
- He finished as the runner-up to Kaká for the 2007 Ballon D'or, and was third in the running for the FIFA World Player of the Year award, behind Kaká and Lionel Messi.
- Ronaldo was named the UEFA Fans' Man of the Match, and wrapped up the campaign with a career-high 42 goals in all competitions, falling just four short of Denis Law's team-record mark of 46 in the 1963–64 season.
- Ronaldo became Manchester United's first Ballon d'Or recipient since George Best in 1968. He finished with 446 points, 165 ahead of runner-up Lionel Messi.
- He became the first Premier League player ever to be named the FIFA World Player of the Year, in addition to being the first Portuguese player to win the award since Luís Figo