Italy, mainland Greece and Denmark are all at risk of being added to the UK's quarantine list this week.
These additions would cause havoc for thousands of Brits abroad, and follow in the footsteps of Portugal.
A rise in infections could see the three countries, currently in the 'amber zone', move to the red zone of countries from which arrivals must self-isolate for 14 days upon return.
Figures show Denmark's cumulative number of cases over seven days at 28.7 infections per 100,000 people.
This is over the Government's threshold of 20 but less than the UK's rate of 31.5.
Italy's new daily cases per 100,000 people are 16.5 and Greece is 15.4, the Daily Mail reports.
The Department for Transport normally announces any additions to the quarantine list on Thursday evening with travellers given until 4am on Saturday to return before the new rules come into force.
New rules from Saturday saw Portugal holidays once again off the cards for Brits after the government warned against all but essential travel the country.
Any travellers returning will need to quarantine for 14 days.
The news came after fears of rising coronavirus cases in the country - but does not include the Azores or Madeira.
Seven of the Greek islands were also added to the quarantine list in England last week.
A DfT spokesman told the Mail: "We keep the data for all countries and territories under constant review and update our exemptions list with any changes on a regular basis."
