The Irons had swooped for the Italian international earlier this week as David Moyes seeks to add a new left-back to his squad before the September 1 transfer deadline to provide competition for regular starter Aaron Cresswell.
After talks with Chelsea, Standard Sport understands that a deal worth an initial £13million plus a potential further £2m in add-ons was close to being agreed between the London rivals.
However, the switch is now off, with West Ham understood to have baulked at Emerson’s high wage demands.
The 28-year-old still has another two years left to run on his well-paid Chelsea contract, but is someone that Thomas Tuchel wants to offload before the window closes.
The Blues also want Billy Gilmour, Ross Barkley, Kenedy and Baba Rahman gone this summer, as well as potentially Callum Hudson-Odoi (only on loan), Hakim Ziyech and Ethan Ampadu. Marcos Alonso is on his way to Barcelona.
West Ham, meanwhile, completed a deal to sign Germany centre-back Thilo Kehrer from Paris Saint-Germain earlier on Wednesday, taking their haul of summer signings to six following the arrivals of Gianluca Scamacca, Maxwel Cornet, Nayef Aguerd, Flynn Downes and Alphonse Areola.
Moyes is still keen to bring in a new left-back, centre-back and central midfielder before the deadline, with the club pushing to sign Belgian international Hans Vanaken from Club Brugge.
They also want to remain in the hunt for Conor Gallagher or Armando Broja in the event that Chelsea allow either player to leave Stamford Bridge on loan late in the window, which would have ruled out a temporary swoop for Emerson, who was believed to favour a switch to the London Stadium over Premier League new boys Nottingham Forest and Serie A side Atalanta.