Andy Carroll could a face up to six weeks on the sidelines with a hamstring injury.
Carroll was forced off with the injury after just 15 minutes in West ham's 3-1 win over Bournmouth yesterday.
The striker had scored two goals in four games for the Hammers since returning from a seven month layoff due to a knee injury.
"He felt he was back and enjoying his football," West Ham manager Slaven Bilic said.
"It's not the end of the world, though. If everything goes well he will be back very soon so there is no reason to be negative.
"If it goes as we expect, then he will be back for a significant part of the season, the last 10-15 games, with enough time to make a huge impact on our season."
