Bournemouth midfielder Lewis Cook has been ruled out for six to nine months after rupturing his anterior cruciate ligament.
The 21-year-old - who was capped by England earlier this year - sustained the injury to his knee during the 2-1 defeat of Huddersfield on Tuesday.
And further assessment and scans on Wednesday have revealed the seriousness of the issue.
Bournemouth boss Eddie Howe said: "We are all devastated for Lewis.
"It is a huge blow to a very talented player, who has been a very important part of our side over the last 18 months."
Cook's Bournemouth team-mate Callum Wilson has been called up by England himself this season, having bounced back from serious injury.
And Howe added: "Lewis is a strong character, who only has to look around our dressing room for inspiration of how an injury like this is merely a setback, and to know that he can come back better than ever.
"He will have the full support and love of everyone at the club throughout the next few months, as he receives the very best treatment and rehabilitation possible."
Cook arrived at Bournemouth from Leeds in the summer of 2016 and has been a mainstay of the squad since then.
He also captained England to U20 World Cup glory in 2017, becoming the first England captain to lift a world trophy since Bobby Moore in 1966.
Cook then won his first senior England cap as a substitute in the 1-1 friendly draw against Italy at Wembley in March.