West Ham want Anthony Martial in exchange for defender Issa Diop, if a deal is to be completed for the highly-rated centre-back [Independent].
The Red Devils have reportedly targeted Diop as a potential new signing this summer, as they look to reassure a leaking defence which last season conceded 54 goals in the Premier League as the club finished in a disappointing sixth-place.
After initial talks, The Hammers have said that they are willing to let the 22-year-old leave, but want forward Anthony Martial as part of the deal.
Having joined the club in 2015 for a fee rising to £58 million, Martial kicked off his career in the Premier League extremely promisingly, gaining comparisons to ex-Arsenal legend Thierry Henry due to his style of play and technique in front of goal.
His time at Old Trafford has been incredibly inconsistent, though, with former manager Jose Mourinho consistently overlooking him during his two-year spell at the club.
It is understood that United are not willing to let the Frenchman leave.
A cash bid of around £60 million will likely be what it takes to prize Diop away from the London Stadium next season - the Red Devils have already seen an offer of £40 million rejected by West Ham.
The 22-year-old impressed during his debut season in the Premier League last term following his reported £22 million move from Ligue 1 side Toulouse.
United have turned to Diop after Leicester City valued their initial defensive target, Harry Maguire, at an astonishing £80 million.
The club were keen on bringing the England international to Old Trafford this summer after his performances for the Foxes during the previous two seasons, but are understandably not willing to part with that sort of money for a defender.
Napoli's Kalidou Koulibaly was also on United's shortlist, but the Serie A club have valued their prized asset at over £100 million, which has again firmly priced them out of a potential deal.
Martial's time in the north west of England has been inconsistent, though there is no doubting that he is still a player of real quality and potential on his day.
At 23 years of age, the France international still has a long career ahead of him; whether or not he is given more of an opportunity under Ole Gunnar Solskjaer next term, though, still remains to be seen.