Sakho picked up a serious looking knock during the 1-1 draw with West Bromwich Albion last weekend and according to reports from the Daily Telegraph, the Hammers fear that they might lose the striker for at least two months due to the injury.
Following the game against West Brom, manager Slaven Bilic has stated that Sakho had suffered a muscle injury.
Bilic said: "The specialist will see him to give an opinion. It looks like a muscle injury and the first news is not the best. It is a big blow.
"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. It is very hard to replace them."