West Ham striker Diafra Sakho will undergo a scan on Wednesday to determine the extent of his thigh injury, according to Press Association Sport.
Sakho, 25, limped off during Sunday's 1-1 Premier League draw against West Brom with a thigh problem, and reports on Monday suggested the Senegal forward would be out for three months.
But PA Sport reports that the exact prognosis is still to be determined after Sakho was injured stretching to shoot into the side-netting during the second half at Upton Park.
West Ham boss Slaven Bilic said afterwards: "It doesn't look good. It's a big blow for us, he's a key player."
Sakho is the third injury problem to hit West Ham's attacking resources after playmaker Dimitri Payet and forward Enner Valencia were hurt against Everton earlier this month.
"You can see injuries in every club and to be fair the number who are missing is not a lot, but the ones missing are key players who play in the same position," added Bilic.
"Valencia, Payet, and now Sakho. It is very hard to replace them."
The Hammers face Manchester United at Old Trafford on Saturday, with Bilic's side sitting in eighth place in the table -- seven points behind table toppers Manchester City.