West Ham want to sign New York Red Bulls centre back Aaron Long but are struggling to complete a deal because he cannot get a work permit at the moment, Sky sources understand.
Long is the MLS defender of the year and has played in six of USA's past seven games, including the Gold Cup final defeat to Mexico earlier this month.
The 26-year-old has a £4m release clause and wants to move to the Premier League, although Marseille, Fiorentina, Rennes and Lyon also want to sign him.
West Ham completed the signing of striker Sebastien Haller from Eintracht Frankfurt on a five-year deal for a club-record fee earlier this month.
The Frenchman's arrival saw the Hammers break their transfer record for the third time in a year, following the signings of Issa Diop and Felipe Anderson