The bid is a huge statement of intent from new boss David Moyes, who has been given the board's backing to spend big.
United were heavily linked with the ex-Arsenal skipper earlier this summer, although Fabregas claimed his intention was to remain with Barcelona.“We haven't got money burning a hole in our pocket”United chief executive Ed Woodward
Moyes then turned his attentions to Fabregas' Barca team-mate Thiago Alcantara, who has now joined Bayern Munich.
But now the Scot has renewed his interest and is willing to hand Fabregas first-team football to boost his chances of starring for Spain at the 2014 World Cup.
Barca are unlikely to let Fabregas go willingly, having nurtured the player through his formative years, only for Arsenal to sign him as a 16-year-old in 2003.
Although he has played 96 times in two seasons, including 60 league games, he has rarely featured in his preferred midfield role due to the performances of brilliant duo Xavi and Andres Iniesta.
Moyes knows that he has to strengthen in the middle of the park.
Finance to back what would be a costly transfer would not be an issue if chief executive Ed Woodward is to be believed.
Woodward said: "We haven't got money burning a hole in our pocket but we have got a strategy on player purchases and if David wants to go after a stellar player he can do that."
At United, Fabregas would be reunited with striker Robin van Persie, who joined from Arsenal a year ago.