The Dutch midfielder is a key target for Erik ten Hag's team this summer, as the new manager looks to stamp his authority on the Old Trafford club.
United had a bid rejected that was valued at around £52 million.
However, the Catalan giants do want to sell de Jong.
The issue is that they must balance their books before they can register new players and make other signings, per ESPN.
La Liga rules mean that only one-third of the money they bring in from transfers can be reinvested in the team.