The France international is paid £215,000-a-week at the Camp Nou and Barca would insist on this being paid in full if United want to take him on a season-long long, according to the Sun.
The Catalan club are willing to let the 23-year-old leave on loan but only if this demand is met and it may prove a step too far for the Red Devils.
Dembele has emerged as a target for Manchester United as a move for Borussia Dortmund’s Jadon Sancho has proved more difficult than expected.
The Bundesliga club have stuck to their guns and demanded £108m for the England winger, a figure that United have been unable, or at least unwilling, to meet.
A loan move for Dembele would prove to be a cheaper option but still an expensive one, given his hefty salary,
The forward has scored just 12 La Liga goals since arriving in Spain and played just nine games in all competitions last season after two serious hamstring injuries.
New Barcelona manager, Ronald Koeman, insisted that Dembele is part of his plans this season, but has not ruled out an exit for him before the transfer deadline on 5 October.
‘The first thing to say is that it is up to the club and to the player,’ he said. ‘But he is with us and as we’ve seen in recent weeks I am counting on him….he has to wait to play but he is training well, getting fitter.
‘I want to say that I am counting on him.’
Dembele has made just one La Liga appearance this season, when he came off the bench in Barca’s 4-0 win over Villarreal last week.