Ben Chilwell is set to miss the rest of the season after deciding to undergo knee surgery, sources have told ESPN.
Chilwell then returned to light training in an attempt to determine whether the partial rupture could be resolved without any need for an operation but sources have told ESPN that a scan on Monday provided a downbeat prognosis and he will be sent for surgery.
The news will come as a significant blow to both Chelsea and England given Chilwell was in fine form having recovered from a disappointing period in which he was an unused member of Gareth Southgate's Euro 2020 squad and initially overlooked at club level in favour of Marcos Alonso.
Chilwell forced his way into favour with both teams, scoring four goals in five games for club and country in October.
He had initially been upbeat about avoiding a lengthy spell on the sidelines after promising early signs but he has failed to make progress in recent weeks.
Chelsea may now opt to enter the transfer market in January to sign cover with Alonso the club's only senior left wing-back.
Speaking after Chilwell first suffered the injury in November, Tuchel said: "There is never a good moment for big injuries and for injuries in general but this for him personally is a very bad moment because he was so involved, so good and so full of confidence.
"He was a huge part in our performances and victories in the last weeks."