Chelsea's full squad have gone into self-isolation after winger Callum Hudson-Odoi tested positive for coronavirus, the club said in a statement.
Hudson-Odoi displayed cold symptoms on Monday morning and has stayed away from the club since then. His test result was returned on Thursday night.
"Chelsea men's team player Callum Hudson-Odoi had a positive test result for Coronavirus returned this evening," the Premier League club's statement said.
"Chelsea personnel who had recent close contact with the player in the men's team building will now self-isolate in line with Government health guidelines.
"These will include initially the full men's team squad, coaching staff and a number of backroom staff."
The club said despite testing positive, the 19-year-old was "doing well and looking forward to returning to the training ground as soon as it is possible".
The Blues have also closed two buildings at their training facility.
Chelsea are scheduled to play at Aston Villa on Saturday afternoon but the match looks unlikely to proceed.
The remainder of the Premier League season, in fact, is in doubt with the League to hold a meeting on Friday to determine a course of action in response to the coronavirus.
