With Spain Under-21 star Thiago set to join up with Pep Guardiola at Bayern Munich, the Red Devils launched a bid to sign the 26-year-old former Arsenal midfielder.
Having seen Thiago elect to join up with former boss Pep Guardiola at Bayern Munich rather than move to Old Trafford, United has turned its attention to the former Arsenal man.
After lodging the offer on Monday, United must now wait for Barcelona to make its stance regarding the midfielder known.
Fabregas often struggled to break in to the Barca lineup last season and was occasionally booed by his own supporters when he performed poorly.
The Gunners have been keeping tabs on Fabregas - who left the Emirates Stadium for Camp Nou in 2011, throughout the summer - and the club has a 29 million euro buy-back clause in place.
Arsene Wenger is keen to bolster his squad this summer and has been in contact with his former midfielder about his current situation in Catalunya.
Despite United's confidence that its 6.2 million pound salary offer would be enough to tempt Thiago, the 22-year-old will complete a move to Bayern Munich this week.