The summer of 2003 was shrouded in uncertainty at Old Trafford. Sir Alex Ferguson had sanctioned the sale of one of his 'Fledglings' in the form of David Beckham to Real Madrid, while his pursuit of Brazilian World Cup star Ronaldinho ended in disappointment.

It meant that the Scottish boss needed to make an addition to his squad that would capture the imagination of the club's supporters.

Step forward an 18-year-old Cristiano Ronaldo, who had turned Manchester United defenders one way and then the other during a recent pre-season friendly while playing for Sporting Lisbon.

The story goes that some of the players pestered Ferguson to recruit to the Portuguese winger and so ten years ago today he arrived in Manchester in a deal worth £12.24m.

Upon signing Ronaldo, Ferguson said: "We have been negotiating for Cristiano for quite some time, but the interest in him from other clubs accelerated in the last few weeks so we had to move quickly to get him.

"He is an extremely talented footballer, a two-footed attacker who can play anywhere up front - right, left or through the middle. He is one of the most exciting young players I've ever seen."

United's new number seven showed his credentials almost immediately during a 30-minute cameo appearance from the bench during the opening match of the Premier League season against Bolton Wanderers. He ended the campaign with six goals to his name, including one in the FA Cup final against Millwall.

With each passing term there was slight improvement, until 2006-07 when he started to produce the type of performances that has made him one of the world's best footballers.

The talk was that he was keen to leave United, fearing a backlash from supporters following his infamous wink which came after Wayne Rooney, his United teammate, had seen red during England's World Cup quarter-final clash against Ronaldo's Portugal.

Ferguson convinced his rising star to stay put though and was rewarded as he scored 23 goals in all competitions, which helped United to regain the Premier League trophy from Chelsea and reach the semi-finals of the Champions League.

Forty-two goals in 49 outings was a major factor behind the Red Devils retaining the title and getting their hands on the European Cup for a third time a year later, although he did miss a penalty during the final shootout against Chelsea.

Despite strong links with Real Madrid, Ronaldo remained with United for the 2008-09 season as they wrapped up a hat-trick of domestic titles. His last encounter in a red shirt would come during that term's Champions League final in Rome against Barcelona, which the Spaniards won 2-0.

In June 2009 and after 118 goals, he was transferred to Madrid for a world record fee of £80m - an amount that is yet to be surpassed. Some speculation has claimed that he could return to United this summer, but as it stands, he is still very much a Los Blancos player.