Borussia Dortmund forward Andriy Yarmolenko has arrived at West Ham's training camp in Switzerland, according to Sky sources.
The 28-year-old has begun the first part of his medical ahead of a £17.5m move to the Premier League side.
Yarmolenko made 30 appearances for Dortmund last season as he helped them to fourth place in the Bundesliga.
If his move if confirmed, he will be the fifth player to move to the London Stadium this summer.
Ryan Fredericks, Lukasz Fabianski and Issa Diop have already joined the club, while Jack Wilshere was also confirmed as a West Ham player on Monday.
The Hammers have been taking part in pre-season training in Switzerland, and played Swiss second-tier side FC Winterthur on Sunday, losing 3-2.