According to Spanish outlet El Pais, the Glazers have changed their asking price mid-negotiation.
Sheikh Jassim was said to be stunned by the decision to ask for more money and has reportedly cooled his interest in the club as a result.
It is suggested that the Glazers upped their asking price to nearer £6billion rather than their initial £5.2billion demand.
Sheikh Jassim is understood to have already tabled four offers for the Manchester club, but there is yet to be any agreement.
The Glazers, who have owned the club since 2005, are also negotiating with Jim Ratcliffe.
Ratcliffe is the Manchester-born billionaire chief of the chemical company, INEOS.
The Glazers would reportedly remain part of Man Utd in minor roles in the deal proposed by the Brit.
The fans are keen to have the current owners removed from the club entirely with long-standing animosity between the Americans and the fanbase.
On the pitch the club have now all but secured Champions League football for next season with only one point needed from their remaining two fixtures.
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Erik ten Hag’s side will also face local rivals Manchester City in the FA Cup final as they try and pull off a domestic cup double following their Carabao Cup victory earlier in the season.
They host both Chelsea and Fulham at Old Trafford before their big day at Wembley on 3 June.