West Ham striker Andy Carroll will be out for at least four to six weeks after tearing a ligament in his knee.
Carroll, playing for the first time since 31 January, picked up the problem in Wednesday’s 0-0 draw at Southampton.
“The medial ligament on the inside of his knee has a little tear from a fairly innocuous collision,” said manager Sam Allardyce on Friday.
“If we’re lucky it could be four to six weeks. It’s a big blow for him and us but one we’ve got to cope with.”
Carroll, 26, was forced to stay on the pitch with the injury because West Ham were down to 10 men and had made all three of their substitutions.
The England striker, out for most of last season with an Achilles problem, missed the first three months of this campaign after injuring ankle ligaments in New Zealand in pre-season but has scored five goals in 14 games since returning in November.
West Ham face West Brom in the FA Cup fifth round at The Hawthorns in Saturday’s early kick-off (12:45 GMT).
Kevin Nolan, Mark Noble and Doneil Henry are back in contention while Guy Demel has returned to training.
Allardyce said: “Our run in the FA Cup up to now has been very good, it’s given us a lot of joy.
“We’d hope to be in a better position squad-wise, but players will have to get through the games as best we can. We’re still producing good performances.
“The West Brom game is about winning, so we have to go there and try to win.”