It is not known if any players have tested positive for COVID-19.
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 is back training and their first game of the Premier League season is at Brighton on 14 September.
On Wednesday Chelsea signed England left-back Ben Chilwell from Leicester for £45m.
He is Chelsea’s third introduction of the summer after the arrivals of winger Hakim Ziyech from Ajax and striker Timo Werner from RB Leipzig.
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