Fati, 17, has featured fairly prominently for the LaLiga champions in his debut season, making 23 appearances, scoring five goals and registering one assist.
The Guinea-Bissau born winger is widely considered as one of the promising talents in world football since graduating from La Masia and has been linked with a move to United and Borussia Dortmund.
It was reported in Spanish media this week that the Blaugrana had rejected a €100m bid from United and according to Sport, Ole Gunnar Solskjaer's outfit is ready to increase their opening bid.
With the teenager holding a release clause of €170m, it's unlikely the Spanish giants accept an offer of anything less, having dubbed him 'untransferable' earlier this month.
The report added that Quinque Setien's side are looking to offer the Spain youth international a new lucrative contract and increase his release clause to €400m, to ward off potential suitors.