Manchester United are in the market for a centre-back this summer and have identified West Ham’s Diop as a player they would like to see in red next season.
The Hammers admit they would be willing to sell the Frenchman for £60m.
Diop is also reportedly keen on a move north seeing it as a progressive step in his career.
Diop only moved to London last summer when he left Toulouse in a £22m deal.
He played 33 times in the Premier League last term, including in his side’s 3-1 win over United in September.
The 22-year-old received plenty of praise from then Red Devils boss Jose Mourinho following that clash.
“Congratulations to the scout that found a 21-year-old kid Diop – a monster who dominated in the duels,” the Portuguese boss said.
Mourinho was axed several months later, but the club’s failure to acquire a central defender – something Mourinho fought hard for – looks set to rear its ugly head 12 months on.
United have expressed a genuine interest in Ajax star Matthijs de Ligt, but the teenager looks set to snub them in favour of a Champions League team.
Leicester’s Harry Maguire, who was a Mourinho target, has continued to grow and remains a player they are keen on.
They face competition from rivals Manchester City for his signature should either of them convince the Foxes to sell.
Diop, however, looks more affordable than both Maguire and de Ligt potentially making him a more attractive proposition.
The Hammers, despite spending around £100m last term, are not readily equipped to challenge the top six.
Their tenth-place finish last term may be bettered, whereas United, who are in a rebuilding phase, will expect to be in the latter stages of most competitions.