Liverpool right-back Nathaniel Clyne faces a lengthy spell on the sidelines after rupturing an anterior cruciate ligament.
Clyne suffered the injury in Liverpool's pre-season friendly with Borussia Dortmund in New York on Friday.
The 28-year-old England international, who spent last season on loan at fellow Premier League side Bournemouth, was sidelined for most of the 2017-18 season with a back injury.
Liverpool manager Jurgen Klopp told the club's official website: "What can I say other than how gutted we all are for Clyney? He was training and playing so well – he was in outstanding shape.
"Clearly an injury of this nature isn't a happy moment for any player, but the silver lining for him is that, according to the medical guys, it's a straightforward ACL injury.
"This means fixing it and coming back from it should follow a path that is free from pitfalls and complications.
"At the moment there isn't much more to say beyond we'll all support Clyney in whatever way we can and we look forward to seeing him back on the pitch as soon as responsibly possible.
"He is such a sound professional and is naturally very fit and strong, so all these things are in his favour."