Mauricio Pellegrino fears that striker Charlie Austin is set to be sidelined for some weeks with a hamstring injury.
Austin was injured in the team's 1-1 draw with Huddersfield Town last Saturday, going off late on after scoring the opener – his fifth goal in five starts.
Pellegrino said the full extent of the problem isn't known, but that the forward is likely to be out for a significant period.
"Charlie will be probably out for a long period of time," said the manager. "It is a little bit more serious [than we first thought].
"But we have to wait and see what the doctors say, in the next few weeks."
Austin was already ruled out of today's match with Tottenham, as well as the visit to Manchester United and home game with Crystal Palace, after being charged by The FA with violent conduct in relation to an incident during the draw with Huddersfield.