The French defender is one of European football’s most sought after young players after emerging as a top talent at Porto.
City were linked with a move for his signature in January, and have since rekindled their interest.
Reports have suggested that the Sky Blues are close to getting the £32m–rated enforcer to the Etihad Stadium, but now United and Chelsea are also keen.
Both clubs want the 23-year-old to slot into their respective backlines, with the Red Devils, arguably, in greater need of his services.
Louis van Gaal has been tasked with replacing veteran duo Nemanja Vidic and Rio Ferdinand, both of whom left for free this summer.
Chelsea have already snapped up promising Frenchman Kurt Zouma, but Jose Mourinho is a big fan of Mangala.
£50m has been raised by the sale of David Luiz, giving ‘The Special One’ funds for additions.