Marko Arnautovic is being sent for a scan on his right foot - an injury which could force West Ham into desperately finding a replacement on Deadline Day.
The 29-year-old striker, who hurt himself during his side's 3-0 loss to Wolves on Wednesday, was later seen leaving Molineux wearing a moon boot and using crutches.
Despite some reports, he did not then get into an ambulance, though the injury is feared to be serious and could rule him out for most of the rest of the season.
It is set to impact how West Ham tackle deadline day on Thursday as the club consider who they could sign to replace their sidelined goalscorer.
Maxi Gomez of Celta Vigo was already identified previously this month when it appeared Arnautovic might leave for the Chinese Super League.
The 22-year-old Uruguayan has a £43.3million release clause but the La Liga side, who are battling relegation, are desperate to keep their star scorer.
Arnautovic decided to end his transfer saga by announcing he would stay at West Ham last week, while he also signed a new one-year deal on Saturday. That was understood to include incentives based on appearances and goals.