Aaron Wan-Bissaka's move to West Ham is reportedly being held up due to a demand the defender has made to Manchester United.
The 26-year-old has made 190 appearances for the Red Devils but the side are open to selling him for £18million, as reported by Mail Sport last week.
Wan Bissaka's current deal expires next summer and United are keen to cash in rather than lose him for free.
West Ham are willing to meet United's valuation but the deal is in a limbo as they can't afford his £90,000-per-week wages according to The Sun.
The same publication claim that Wan-Bissaka is open to joining the Hammers but has no huge desire to leave United and is unwilling to sell himself short.
The right-back would be able to cash a significant sign-on fee next summer if he runs down his United contract.
His representatives are pushing United to give Wan-Bissaka a sum of the £18m fee to ensure the deal goes ahead successfully.
Should United sell Wan Bissaka, they would then look to hold further negotiations with Bayern Munich for right-back Noussair Mazraoui.
West Ham nearly signed Mazroui after agreeing a fee of £12.6million plus £2.3m in add-ons with Bayern for the Morocco defender before the deal collapsed.
Meanwhile, Erik ten Hag's side saw a joint bid for Mazroui and his bayern team-mate Matthijs de Ligt rejected last week.
United could also sign a left-back after Luke Shaw missed large chunks of last season through injury and Tyrell Malacia didn't feature at all after double knee surgery.
The Dutchman has resumed fitness training at Carrington but did not join the pre-season tour to the US.
United have spent £59m on Leny Yoro, who was injured in the defeat to Arsenal in LA in the early hours of Sunday, and still want to add another central defender. Talks continue with Bayern over De Ligt after Everton rejected a second offer of £50m for Jarrad Branthwaite.