Brentford have reached a verbal agreement with West Ham to sign defender El Hadji Malick Diouf in a deal worth up to £40m.
The 21-year-old Senegal left-back would cost an initial £35m, with a further £5m in add-ons.
West Ham have accepted Brentford’s bid and Diouf has been cleared to have a medical.
Diouf played in West Ham’s Championship opener against Burnley, but has been excluded from the matchday squads of the Hammers’ past two games.
He has been the Bees’ priority defensive target in this transfer window, but discussions had stalled this summer before being reopened this week.
Diouf would return to the Premier League after suffering relegation with the Hammers last season.
And his sale would represent a big profit for West Ham on a player they paid £19m for a year ago to join from Slavia Prague.
Diouf played 34 times for West Ham last season, providing five assists.
He could become Brentford’s fifth summer signing of the summer after the arrivals of striker Callum Wilson, midfielder Mamadou Sangare, centre-back Jannik Schuster and winger Jaidon Anthony.
After breaking into the Senegal side last year, Diouf played four times at the World Cup this summer.
While West Ham were relegated after finishing 18th last season, Brentford enjoyed an excellent campaign under Keith Andrews, finishing ninth and just missing out on European football on goal difference.
Brentford began their season on Saturday with a 3-0 win over Tottenham Hotspur, and play Leeds on Sunday in their next league game.