The Premier League champions have been knocked back so far in their pursuit of the former Arsenal star.
According to The Mirror though, David Moyes will make one final attempt to lure Fabregas back to England, with a £40m bid.
United believe that the uncertainty over the Spaniard's starting spot at the Camp Nou could still help them sign him.
Fabregas started Barca's first game of the season against Levante, but was left on the bench for the midweek Super Cup game against Atletico Madrid, and is reported to be worried about his place in the team.
If United fail to land the Spain international, they will turn their attention to Luka Modric, who is reportedly interested in returning to the Premier League, while fellow Real Madrid midfielder Mesut Ozil is also said to be available.