A number of Chelsea players are in quarantine after returning from their summer break.
It is not known if any players have tested positive for coronavirus.
Players who test positive for Covid-19 must self-isolate for 10 days and return a negative test before resuming training.
Those who return a negative test but have been to a country not on the government’s travel corridor list must spend 14 days in quarantine.
Chelsea are back training and their first game of the new Premier League season is at Brighton on 14 September.
On Wednesday they signed England left-back Ben Chilwell from Leicester for £45m.
He is Chelsea’s third addition of the summer after the arrivals of winger Hakim Ziyech, 27, from Ajax and striker Timo Werner, 24, from RB Leipzig.