[4] He played with Calgary Foothills as a youth before beginning his professional football career in Germany with Bayern Munich.

As a Canadian citizen with a Welsh mother and an English father, Hargreaves was eligible to represent Canada, Wales or England.

[6] His father played football for the Bolton Wanderers youth side[7] and also for the Calgary Kickers of the Canadian Soccer League.

On 12 August 2000, Hargreaves played in his first Bundesliga match against Hertha Berlin, making an appearance as a substitute for Carsten Jancker in the 83rd minute.

He made 46 appearances in all, with the club finishing third in the Bundesliga, making the quarter-finals of the Champions League and being defeated in the DFB-Pokal by Schalke.

After clinching the double the year before, the Bavarian side finished second in the Bundesliga, and were knocked out of the Champions League by Real Madrid.

However, Bayern were knocked out in the quarter-final by Milan and finished fourth in the Bundesliga, missing out on Champions League football for the first time since 1996.

He made his first Premier League appearance in United's third game of the season, in the derby match away to Manchester City in a 1–0 defeat.

The start of Hargreaves' second season at United was hampered by injury, a recurring patellar tendinitis problem that restricted him to sporadic appearances in 2008–09.

After trips to specialists in both London and Sweden yielded no results, Hargreaves travelled to Colorado, USA, in November 2008 to visit renowned knee surgeon, Richard Steadman.

[25] In January 2010, it was speculated that Hargreaves was slated to return in time for United's Champions League first knockout round tie against Milan, despite not being fully match-fit.

[26] However, on 4 February, Hargreaves suffered a major setback to hopes of playing in the 2010 FIFA World Cup as Alex Ferguson omitted him from the squad for the knockout stage in favour of Belgian defender Ritchie De Laet.

[29] He eventually made his comeback a week later, playing for 45 minutes of United's reserve team match against Burnley on 18 March.

[34] On 6 November 2010, he made his first start since September 2008 against Wolverhampton Wanderers, however it was short-lived after a hamstring injury forced his withdrawal for Bébé just five minutes into the match, which United went on to win 2–1.

[38][39] Buoyed by Richard Steadman's optimistic assessment that Hargreaves' knees, a source of injury for a number of years, could withstand the impact of 'jumping from the Eiffel Tower',[40] a number of clubs including Bolton Wanderers Aston Villa,[41] Tottenham Hotspur,[41] Leicester City,[42] West Bromwich Albion,[43] Nottingham Forest[43] Queens Park Rangers,[42][43] Rangers,[42][43] and "several MLS clubs",[42][43] were believed to be considering an offer for Hargreaves.

[45] On 30 August 2011, Hargreaves was pictured supposedly having a medical with Manchester City doctor Phillip Batty ahead of a move to the club.

[46] City had been looking for a replacement for Patrick Vieira who retired the season before and an additional midfielder due to Yaya Touré's anticipated absence during January 2012 because of the 2012 Africa Cup of Nations.

[53] City were to be victorious in the Premier League, winning their first English title for 44 years, with Hargreaves being involved in the on-pitch celebrations after defeating Queens Park Rangers on the final day.

[6] Hargreaves was not selected to play for the Canada U-17 World Cup team, despite being a promising youth player who trialled for Bayern Munich and was about to sign a contract with them.

Hargreaves was the only player playing outside the Premier League to be selected for England's 2002 FIFA World Cup squad.

Although he had not usually been part of the first-team, he was selected for the England squads at Euro 2004 in Portugal and the 2006 World Cup in Germany despite criticism from sections of the press and public.

The generally negative perception of him by English fans had not been helped by his seeming to have an essence of "German-ness", exacerbated by his Canadian accent and fluency in German.

"[67] Hargreaves' career was affected by injuries, the bulk of which formed in 2006, the year he won the award for England's best player at the 2006 World Cup.

Speculation rumbled about Hargreaves retiring due to his injuries[74] but determined to prove himself, he uploaded YouTube videos of himself training to convince potential clubs of his fitness.

He believed that his prolonged trouble with injuries were due to the revolutionary treatments he was forced to undergo in an effort to solve a problem he felt had been exacerbated by the injections.