Javier Hernandez will fly to London on Tuesday to have a medical and complete his move to West Ham, Sky sources understand.
The 29-year-old Mexico international will become the highest-paid player in the club's history and is set to be on wages totalling £140,000 a week.
The Hammers agreed terms with Bayer Leverkusen on Thursday, releasing a statement confirming the forward was due in London "in the coming days" to complete the formalities of his move.
'Chicharito', as he is known, spent four seasons with Manchester United between 2010 and 2015, where he scored 59 goals in 156 appearances, before going on loan to Real Madrid in the 2014/15 campaign.
The two-time Premier League winner left Old Trafford in August 2015 for Germany, where he has been even more prolific, netting 39 times in 76 matches for Leverkusen.
West Ham have made three signings so far this summer, confirming Stoke midfielder Marko Arnautovic for a club-record fee on Saturday, while Pablo Zabaleta joined on a free transfer and Joe Hart on a season-long loan from Manchester City.