The Government has urged holidaymakers to "keep an eye out" for changes to the travel quarantine list, amid increasing speculation Croatia could be included after a rise in coronavirus cases.
The Department for Transport (DfT) said an announcement could be made this week about changes to the UK's list of safe travel corridors, with people returning from countries not included required to self-isolate for 14 days.
A significant increase in Covid-19 infections across Croatia in recent days means it may follow France in being removed from the safe travel list.
The number of cases per 100,000 people in Croatia has reportedly risen above 20, which is seen as a key benchmark.
A DfT spokesman declined to comment on Croatia, but told the PA news agency travellers should be aware the safe travel list could change this week.
The Balkans region is considered a "hotspot" for coronavirus by the World Health Organisation (WHO).
Dr Catherine Smallwood told a WHO press conference: "The situation in the Balkans has been a concern of ours since early June when we started to see cases increase and it's been very much a sub-regional hotspot over the summer period.
"We really need communities to take this on board, take the adequate steps both at a country level, in terms of the basic contact tracing, case identification and isolation and testing the systems that need to be in place.
"And then where there are hotspots and increased transmission, additional targeted measures need to be brought in place very quickly to nip transmission in the bud, stop it from spreading and keep the level of transmission at controllable levels."
The Foreign and Commonwealth Office also said travellers should "keep tabs" on any DfT announcements regarding travel corridors.
A spokesman said: "We are monitoring the international situation very closely and keeping our travel advice under constant review so that it reflects our latest assessment of risks to British people.
"Anyone wanting our latest travel advice updates can sign up to alerts on the FCO website or follow our Travel Advice social media accounts."