The Hammers were pursuing the Manchester United star after a £30million deal was agreed last week.
However, West Ham have since slammed the brakes on the deal after growing tired of waiting for his Old Trafford exit to be finalised.
talkSPORT understands they are threatening to walk away from the deal for good with the club already pursuing alternative centre-back targets.
Man United are still open to selling the player and have offered to hand Maguire a £6million pay-off in order to complete the move, but the England star is yet to accept.
The 30-year-old has two years on his current contract which is worth £190,000 a week and was limited to just eight starts in the Premier League last term.
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The writing looked to be on the wall for Maguire after he was stripped of his captaincy earlier this summer, but speaking last week, Erik ten Hag said he'd be happy for the defender to stay providing that he was content with fighting for his place in the team.
Ten Hag said: "For Harry, that is just how I described it. He has to fight for his place.
"He has the ability to be a top-class centre-back and he is the best for England so why shouldn't he be the best for us? But he has to prove it.
"When he is not confident enough to fight then he has to go. Then he has to make a decision, but I'm happy with him."