The Hammers believe they have a full agreement with Man United, while personal terms with the player are not expected to pose a concern.
However, the transfer has not progressed as Maguire wants the difference in his salary covered by the Red Devils.
Hammers manager David Moyes is keen to add Maguire to his ranks, and West Ham are still willing to make the transfer happen.
However, they will be forced to explore other options if Maguire and Man United do not resolve the contract dispute soon.
The 30-year-old centre-half was an unused substitute in Man United’s opening day 1-0 victory over Wolverhampton Wanderers on Monday night.
Man United manager Erik ten Hag has always maintained that he is happy for players to stay at the club and fight for their place.
However, Maguire’s four-year chapter at the Theatre of Dreams looks set to end this summer, assuming the pay-off issue is resolved in time for the deal to be finalised.
The delay in Maguire’s exit could also have implications on further incoming transfers at Man United, with a potential replacement for the Englishman already lined up.
The Red Devils have shortlisted several names but have opened talks with Bayern Munich over a deal to sign Benjamin Pavard.
The Frenchman is eager to leave the German champions this summer despite reluctance from the club to sanction a deal.
The World Cup-winning centre-half has one year left on his existing deal at the Allianz Arena but talks over an extended contract have yet to unfold.
The Premier League giants are only willing to go as high as €35m, while an agreement on personal terms with Pavard is expected to be a formality.
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