Chelsea midfielder Ruben Loftus-Cheek has ruptured his Achilles tendon and will have surgery on Thursday night.
The club announced that the England international suffered the injury during the 3-0 friendly win over New England Revolution in Boston on Wednesday.
The 23-year-old will now miss the Europa League final with Arsenal, as well as England's summer Nations League commitments.
With the Premier League season over and the Europa League final not until the end of the month, Chelsea were in America for a friendly to promote the club's Say No To Antisemitism campaign.
Prior to the fixture, manager Maurizio Sarri lauded the trip's purpose, but conceded that he felt his men needed to rest.
Nevertheless, the Italian fielded a strong starting XI at the Gillette Stadium in Foxborough, Massachusetts, where owner Roman Abramovich was in attendance on Wednesday night.
"We go there for a good reason I think, so as a man I am very happy to go there," Sarri had said.
"As a coach, of course, I am a little bit worried because I know very well that the team now needs rest. So it is not the best way to prepare for the final, I think."
Loftus-Cheek's injury mirrors the one suffered by club and international team-mate Callum Hudson-Odoi last month.
Speaking about Loftus-Cheek, who had a growing influence on Chelsea towards the end of the season, England boss Gareth Southgate said on Thursday: "I went to bed last night and Ruben's in the squad and playing brilliantly.
"He misses now a major European final and a brilliant opportunity for us."
Five players who have suffered serious Achilles injuries like RLC
We take a look at five players who have suffered similar injuries and how they have fared afterwards.
- David Beckham
England midfielder Beckham missed the 2010 World Cup in South Africa after tearing his Achilles while playing for AC Milan on loan from LA Galaxy. The then 34-year-old made a full recovery and played for another three years before ending his illustrious playing career at Paris St Germain in 2013.
- Laurent Koscielny
Arsenal defender Koscielny might have had a World Cup winners' medal among his collection had it not been for the ruptured Achilles he suffered in last season's Europa League semi-final against Atletico Madrid. The France international spent seven months on the sidelines, but returned to action in December last year and has since re-established himself in the Gunners' starting line-up.
- Jonathan Walters
Republic of Ireland international Walters called time on his career in March after finally admitting defeat in his efforts to bounce back from a partially-ruptured Achilles tendon. The 35-year-old Burnley striker picked up the injury after coming on as a substitute at Bolton in September last year during a loan spell at Ipswich, and was initially expected to be sidelined for six months.
- John Barnes
Liverpool and England winger Barnes suffered a second Achilles rupture on England duty in Finland in June 1992 and missed both the FA Cup final and the European Championship as a result. Surgery left him with a sizeable scar and on his return some five months later, the blistering pace which had helped to make his name had gone.
- Neil Webb
England midfielder Webb was floored by a snapped Achilles just weeks into his Manchester United career after making a £1.5million switch from Nottingham Forest in 1989. He spent seven months on the sidelines, but struggled to return to his best during his three years or so at Old Trafford and on his return to Forest before dropping down the divisions.