Blues want Hammers ace and two more before transfer window closes.
Chelsea look set to launch a £21m bid to sign West Ham United forward Enner Valencia before the end of the January transfer window, according to the Sun.
The Blues want to bolster their attacking options this winter, with Andre Schurrle widely expected to be leaving the club after falling out of favour with manager Jose Mourinho.
Valencia only joined West Ham this summer, but has caught the eye of Chelsea as they look to continue their fine run of form this season that has seen them become strong favourites to win the Premier League title.
The Blues are also still in talks over a deal to sign Fiorentina winger Juan Cuadrado in another fine move upfront, while Shakhtar Donetsk star Douglas Costa is yet another attacker being strongly linked with the club.
Cuadrado should cost around £27m, Costa a further £22m, while Chelsea hope to land Valencia from their London rivals for around £21m.