Diop, 21, was born in Toulouse and has come up through the ranks with his hometown club, making more than 80 first-team appearances for the French side since his 2015 debut.
At 6ft 4in tall, Diop is an imposing figure at the back, possessing superb strength and aerial ability, whilst his turn of pace means he is unsurprinsgly attracting interest as a well-rounded centre back.
That would be a major boost for new Hammers boss Manuel Pellegrini, but The Mirror report that Everton are still keen and could yet attempt to hijack the move.
Everton – now led by new director of football Marcel Brands and new manager Marco Silva – are looking for defensive reinforcements, given that Ashley Williams and Phil Jagielka are deteriorating at the wrong side of 30.
Diop would fit the bill for the Toffees, and whilst West Ham have a headstart on negotiations, no deal is competely finalised just yet, given Everton hope of a late transfer steal.