West Ham midfielder Manuel Lanzini could be out for up to six weeks with a thigh injury.
The Argentine, 22, suffered the problem in training before Saturday's 0-0 draw at Manchester United.
Lanzini, on a season-long loan from Abu Dhabi club Al Jazira, has four goals and one assist in his 12 league appearances this campaign.
He had a scan on Monday and has now begun the rehabilitation which should see him return next month.
Meanwhile, Hammers winger Victor Moses will have a scan on Tuesday on his hamstring injury.
The 24-year-old, on loan from Chelsea, came off during the goalless draw at Old Trafford.