West Ham midfielder Lucas Paqueta could be sidelined for "at least two months" with a calf injury.
The Brazilian suffered a recurrence of the issue in Sunday's FA Cup draw with Bristol City, having initially been injured against Arsenal at the end of December.
He missed the goalless draw with Brighton on 2 January and lasted just 14 minutes of the Bristol City tie.
Paqueta is set to see a specialist to determine the extent of the problem.
His absence would be a major blow for manager David Moyes as Paqueta emerged as a key figure in West Ham's resurgence during 2023.