The Hammers agreed a fee with Brentford for the Algeria international and started to put him through his medical paces ahead of completing the transfer.
However, they have unearthed an issue in the medical and it has been claimed that the transfer is now in serious danger of falling apart.
West Ham are looking to renegotiate the fee for Benrahma, given the medical results.
And sources close to the winger are confident that the move to West Ham will eventually go through before the domestic window closes this evening.
They are confident that Benrahma, who wants to play in the Premier League, will become a West Ham player.
The winger has also been attracting interest from other Premier League sides, but there is as yet no sign of another club trying to hijack West Ham’s swoop.
It remains to be seen if West Ham can come to a new agreement on a price with Brentford.