El Hadji Malick Diouf is set to join Brentford from West Ham.
Standard Sport understands a deal is close to being finalised after the Bees agreed to pay the Hammers a fee that could, including add-ons, be worth £40million.
The player has been given permission to undergo a medical.
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Brentford are understood to be paying around £36m up front.
A five-year contract has been agreed for the Senegalese left wing-back, whose sale will provide the Hammers much-needed funds as they approach deadline day and bid to earn promotion from the Championship and a return to the Premier League.
Diouf was always keen on the move to Brentford but did also field interest from Crystal Palace this summer.
It was last month that Brentford enquired about his price before talks went cold for around a month.
After negotiations reopened in the last few days, an agreement on the fee has now been reached in club-to-club talks as the deal nears completion.
Brentford have bolstered their squad this summer, with Jannik Schuster, Jaidon Anthony and Callum Wilson all signing before the club smashed their transfer record to bring in Mamadou Sangare from Lens.
When asked after the 3-0 win over Tottenham at the weekend if a fifth new arrival was on the cards before the window closes, Keith Andrews said: "I'd have to say I'm very content with the squad.
"I think the squad depth right now is as good as it's been. You see the types of subs that we've brought on today, the energy and the quality that brings onto the pitch.
"The starting line-up will obviously change as the season goes on, so that depth is important. If the window closed tomorrow, I'll be pretty happy."
