Diafra Sakho has handed in a transfer request at West Ham, according to Sky sources.
The striker was the subject of a failed £11m bid from Sunderland last month.
Black Cats manager Sam Allardyce brought the Senegal international to Upton Park from Metz in 2014 when he was in charge of the Hammers.
The 26-year-old joined on a four-year contract and has scored 15 goals in 43 Premier League matches for the club.
West Brom are reportedly interested in Sakho, who complained of illness and stayed in the UK when the rest of the West Ham squad flew to the US for their pre-season tour at the weekend.
The forward, who reportedly fell out with the club in April after being named on the bench, has grown further unsettled due to West Ham admitting they want to sign a big-name striker.