Ruben Loftus-Cheek could be out for a year after the Chelsea midfielder ruptured his Achilles during the friendly against New England Revolution in Boston.
The England international was seen leaving the Gillette Stadium on crutches and will now almost certainly miss the Europa League final in Baku on 29 May.
The Sun have sensationally claimed Loftus-Cheek faces a minimum of six months on the sidelines, with the injury confirmed to be worse than teammate Callum Hudson-Odoi's.
The former Crystal Palace loanee will be monitored by Chelsea medics as they assess the damage, but is believed that if their worst fears are confirmed he could miss up to a year of action.
The injury also looks set to rule the 23-year-old out of England's UEFA Nations League semi final against the Netherlands in early June.
Loftus-Cheek has slowly become a key player for Chelsea over the course of the season, playing a key role in their run to the Europa League final, but is now likely to be replaced in Maurizio Sarri's starting lineup by either Mateo Kovacic or Ross Barkley.
He played a large role in helping Chelsea secure a top four spot, ending up as the club's third highest scorer in the league after strikes against Brighton and Watford saw him reach six for the season.
Loftus-Cheek has been the subject of transfer speculation throughout the campaign due to Sarri's initial reluctance to start him regularly, but the midfielder seems to have gained the Italian's trust thanks to some classy displays towards the end of the season.