The BBC Grand Prix has been suspended this year and Formula 1 is assessing the possibilities of replacing the race, BBC Sport can reveal.
F1 and the Singapore authorities agreed that it would not be possible to hold the event in connection with immigration restrictions in the city-state.
Other races later in 2021 could also become prey for the coronavirus pandemic.
Turkey, China and another race in Austin, USA are all being considered as replacements.
“We understand that our fans were looking forward to another edition of the Singapore Grand Prix,” said Colin Syn, vice-president of the race.
“Canceling the event for the second year is an incredibly difficult decision, but a necessary decision in light of the current restrictions on live events in Singapore.”
Singapore is one of the countries that has managed the pandemic and kept infections low by strict immigration restrictions and a comprehensive test-and-tracking system.
And authorities who have decided that their control measures are not compatible with thousands of people entering the country for a grand prix.
What could replace Singapore?
One option being considered by F1 as a replacement is a race in Turkey’s Istanbul Park.
Turkey was scheduled to replace the Canadian Grand Prix this month, but had to be canceled two weeks after it was put on the calendar as an increase in coronavirus cases in the country led to it being placed on Britain’s red list of restricted countries.
A revival of the Chinese Grand Prix, which was postponed from the date of the early season this year, is also possible.
And F1 has been offered the opportunity by the Circuit of the Americas in Austin, Texas to hold two races.
If that happens, the first race is likely to be on the 15th-17th. October, the weekend before the American Grand Prix, which is the 22nd-24th. October.
This would be a particularly appealing opportunity for F1’s owners, the American group Liberty Media.
What other breeds are in doubt?
Although F1 is still targeted at a full 23-race calendar, the Japanese, Brazilian, Mexican and Australian Grand Prix are in doubt for various reasons.
Japan is moving forward with the Olympics this summer despite an increase in Covid cases that have led to the imposition of emergency measures in the capital Tokyo and other parts of the country.
Organizers in Suzuka are currently expecting the race, but will make a full assessment when the Olympics are over.
Mexico and especially Brazil have among the highest cases of coronavirus in the world, but are determined to hold their races and believe that they can protect F1 staff by keeping them away from the local population by assigning specific hotels and organize public transport to and from the track.
But if one of the countries were put on Britain’s red list, it would make their race very problematic.
Australia, like Singapore, has opted for a zero-tolerance approach to the travel pandemic, with major travel restrictions.
The plan for the Melbourne race is for vaccinated staff to enter the country for the race and be able to escape full-time quarantine at hotels when they are not on the track.
But the concern is about what would happen if there was a positive case among F1 staff while out in Australia.
Currently, a positive case in Melbourne triggers a deadlock across the city, and F1 is worried that a case in the paddock – which so far this season has been handled by the sport’s isolation protocols – would lead to authorities canceling the race.
F1 will likely have insurance policies on that front before committing to travel to Australia.
Vaccinations are also likely to become a problem with an increasing number of races as the season continues.
The sport has known for several months that some placements will require vaccines and track the number of teams and F1 that have them.