West Ham striker Danny Ings suffered a knee strain on debut in victory over Everton.
West Ham bought Ings for 12million last week to boost their goalscoring threat and his injury will be a huge frustration for David Moyes, who is set to be without the striker for at least a few weeks.
Igns has been ruled out of next Monday's FA Cup trip to Derby and is expected to miss Premier League games against Newcastle on February 4 and Chelsea on February 11.
West Ham are optimistic the injury is not serious and hope the 30-year-old could be back to face Tottenham on February 19.
Ings has suffered two major knee injuries in the past but his latest injury is not linked to those.