West Ham's £20million record signing Andre Ayew could be sidelined until Christmas with a thigh injury.
The Ghanaian striker lasted just 35 minutes of his debut against Chelsea on Monday before limping off.
West Ham, currently in Romania ahead of their Europa League qualifier against Astra Giurgiu on Thursday, were awaiting the results of a scan on the injury.
But Jack Sullivan, the son of West Ham joint-chairman David Sullivan, wrote on Twitter: "We are devastated that Ayew will be out for about 4 months. He needs surgery."
The news will be a major blow for manager Slaven Bilic, who had spent all summer attempting to bolster his attack before finally landing Ayew last week.