Sakho became the first West Ham frontman to score this season when he found the net in Sunday's draw at Manchester United.
It was only the Senegal international's second appearance of the season following a long spell out injured, but he could now face another four weeks on the sidelines with a hamstring problem.
With Andy Carroll and Andre Ayew having missed the majority of the campaign and summer signings Simone Zaza, Jonathan Calleri and Ashley Fletcher all misfiring in front of goal, manager Slaven Bilic has another headache ahead of Wednesday's return to Old Trafford in the EFL Cup.
"The scan will show us how bad the injury is," said Bilic. "We don't know yet but he definitely won't play tomorrow. If it's one week, two weeks, four weeks, I don't know.
"It's a big blow for us. He showed against Spurs and against Manchester United what he brings to the team. I can only hope it's not going to be long."