West Ham defender Aaron Cresswell will miss the start of the season after being ruled out for up to four months with a knee injury.
The 26-year-old left-back, one of the Hammers' most consistent performers last term, suffered ligament damage in their pre-season friendly win over Karlsruher in Austria on Saturday.
Cresswell will see a specialist in London next week to determine whether or not he requires surgery.
West Ham's medical chief Stijn Vandenbroucke told the club website: " Whatever course of action we decide to take, Aaron faces a period of rest, followed by treatment and rehabilitation and he will be out for a period of between three and four months."
The news comes as a blow to manager Slaven Bilic, who is short of cover at left-back, as well as to the player himself as he was touted for a place in Sam Allardyce's first England squad in September.
Allardyce was the man who signed Cresswell for West Ham two years ago and remains an admirer.
The Hammers are also waiting to assess a knee injury suffered by midfielder Manuel Lanzini, who was due to play for Argentina at the Olympics .
"We are in close contact with Manuel and the AFA (Argentine Football Association), who have started a late-release replacement procedure with the IOC," added Vandenbroucke.
"Until he has been assessed by the IOC, he cannot be replaced, but after this process has been completed we want him to return to England to be assessed by our own medical staff as soon as possible."