The Vietnam Grand Prix is under threat because of the coronavirus outbreak.
Vietnam's first Formula 1 race is scheduled to be held on 5 April but the country has said it will refuse entry to anyone who has been to Italy in the previous 14 days.
That would mean Alfa Romeo's Antonio Giovinazzi and personnel from Ferrari and Alpha Tauri and tyre supplier Pirelli could not enter the country.
F1 boss Chase Carey is in Vietnam, trying to ensure the race goes ahead.
But if the Vietnamese government refuses to waive restrictions then the race will have to be postponed as F1 has made it clear no grand prix can happen if personnel from any team cannot get there.
Vietnam has said that anyone who has visited Italy, China, Iran or Daegu city and Gyeongsangbuk province in South Korea in the previous 14 days will be refused entry to the country.
The only exceptions are for people with "specific agreement travelling on official government business".
If Vietnam has to be called off, F1 will probably look to reschedule the event later in the year.
But the practicalities involved and the uncertainty surrounding the coronavirus outbreak could make that impossible.
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Vietnam would be the second grand prix that has had to be rescheduled this year, after the Chinese Grand Prix was postponed in February from its 17 April spot.
F1 has looked at rescheduling it, but so far no alternative date has been agreed.
There remains uncertainty about the rest of the calendar as countries seek to slow down the progress of the virus outbreak, which on Wednesday was declared a pandemic by the World Health Organisation.
There are questions over the season-opening Australian Grand Prix in Melbourne this weekend after a total of five team personnel - four from the Haas team and one from McLaren - were advised to go into isolation in their hotels after developing symptoms that could be related to coronavirus.
It remains to be seen what officials and local government will do if any of the three test positive for Covid-19, and whether the race will still be able to go ahead.
Results are expected at some point on Thursday.
Dr Brett Sutton, the chief health officer for the state of Victoria, said: "I'm aware that there's a crew who are unwell and in isolation who have tests pending. It'll depend on those tests.
"If they are negative and haven't exposed other crew, then I can say that they can carry on. But if there are positive crew and they've exposed a number of others then all of those contacts need to be in quarantine and so it'll be a question of whether they've got the operational staff to continue.
"I've spoken to my team about getting those test results as soon as possible. It's really contingent on that.
"If there are positive tests, then I'll be directly involved with the (Australian Grand Prix) CEO, with the organisers around what next steps need to be taken, what the implications are."
As increasing numbers of sporting events are postponed or cancelled as a result of coronavirus, F1 has come under increasing pressure over the way it has handled the situation.
But Williams deputy team principal Claire Williams said that she believed F1 and governing body the FIA had so far "done the best job to act responsibly" over the coronavirus.
Both organisations are having daily meetings and are taking their lead from local governments in countries where races are due to be held.
Williams said that, in the event of a positive test for Covid-19 from anyone in the paddock, the ultimate decision as to whether the race proceeded this weekend would rest with the Australian government.