West Ham boss David Moyes is hopeful of Maxwel Cornet's injury not being serious.
Cornet, who suffered a calf injury while doing his defensive duty against Wolves, is out of tonight's Europa Conference League tie with Anderlecht.
Moyes said, "Everybody has travelled except for Maxi Cornet, who has a little bit of a calf strain.
"We don't know how long it'll keep him out for the moment – we don't think it's too severe but he hasn't travelled.
"It's difficult for him because we want to get him up to speed and he didn't have many pre-season games so we're trying to edge him towards it. He's actually had a contribution in quite a few of our games recently and these are the sort of games where we're talking about a chance to give these boys an opening, but we haven't got him for this one."