Sheikh Mansour, a member of Abu Dhabi's ruling Al-Nahyan family reportedly worth £20billion, has invested heavily in City since the 2008 takeover and has been rewarded by seeing the team qualify for this season's Champions League and win the 2011 FA Cup.
City have also made a positive start to the 2011/12 Premier League season which has put them on course to challenge Manchester United for the domestic title.
FourFourTwo say that Usmanov is now wealthier than QPR shareholder Lakshmi Mittal. The Uzbek businessman is now reported to be worth £12.4bn, with Indian steel magnate Mittal slipping to third with a fortune of £11.8bn.
Chelsea's Russian billionaire owner Roman Abramovich sits fourth on the list, with FourFourTwo reporting his fortune grew by £2.9bn over the year to reach £10.3bn.
Malcolm Glazer, the controversial owner of Manchester United, has reportedly increased his fortune by £110million to remain ninth on the list.
Liverpool owner John W Henry, whose consortium completed their buy-out of the club just over a year ago, is the highest new entry on the list, with the American going in at 20th.
Former England captain David Beckham's wealth has grown by £35m to give him a personal fortune of £135m according to the FourFourTwo list, making him the wealthiest player on their list and 42nd overall.
Michael Owen and Rio Ferdinand remain second and third on the players' list, with Ferdinand's United team-mates Ryan Giggs and Wayne Rooney fourth and fifth respectively.
England boss Fabio Capello's reported fortune of £38m puts him top of FourFourTwo's managers list.