West Ham have confirmed Aaron Cresswell could be facing up to six months on the sidelines after injuring his knee during the 3-0 preseason friendly victory against Karlsruher.
Cresswell, 26, has missed only one Premier League match since signing for West Ham from Ipswich in 2014.
The defender required treatment following a challenge from Karlsruher midfielder Grischa Promel, but eventually left the pitch on his feet with the assistance of West Ham's physio.
Following the game Hammers boss Slaven Bilic said: "The only downside of this game is that we have to see what is [wrong] with Cresswell. He got injured and it didn't look that good. We will have to assess it."
West Ham fan site Claret and Hugh then reported the injury could leave Cresswell out of action for six months, something co-chairman David Gold confirmed on Twitter.
CandH sources are accurate and we are apprehensive but it doesn't look minor. We await the scans in the next day or so good luck Aaron. dg
- David Gold (@davidgold) July 24, 2016
He said: "CandH sources are accurate and we are apprehensive but it doesn't look minor. We await the scans in the next day or so good luck Aaron. DG."