West Brom, Southampton and at some stage Everton were all believed to be in the hunt for the 25-year-old Italian international.
West Ham manager Slaven Bilic is believed to be keen to sign a forward after Simone Zaza departed for Valencia and his pursuit of Jermain Defoe and Scott Hogan all but over.
Napoli are reported to be demanding a minimum of 20 million euros for the forward who has had an impressive first half of the season in Serie A.