West Ham have suffered another injury setback with Winston Reid and Victor Moses facing up to six weeks on the sidelines with hamstring problems.
Centre-back Reid was injured during training and will get the results of a scan on Friday.
"It doesn't look good," said Hammers boss Slaven Bilic.
"It's one of those they tell you is four to six weeks but it doesn't look like a small one. He slipped and felt it rupture."
Moses, on loan from Chelsea, suffered his injury in a goalless draw at Manchester United last weekend.
The pair join a growing injury list at West Ham with attacking midfielder Dimitri Payet and striker Diafra Sakho out until February, while Manuel Lanzini is out for six weeks with a thigh problem also suffered in training.
Bilic added: "Victor is out for four to six weeks. It's a blow, we have had six injuries since the Everton game.
"Before that we had a full squad, then Payet and Valencia were injured against Everton and now we have four muscle injuries."
Bilic could have Enner Valencia back to face Stoke on Saturday after the striker's five-week absence with an ankle injury.
However, the Hammers boss has moved a switch of training grounds forward in a bid to help alleviate the club's injury problems.
"We will be training at Rush Green from Monday," said Bilic. "The pitches here at Chadwell Heath are soft on top, but hard underneath which is the worst combination.
"So I have made the decision to go to Rush Green where the pitches are better."