Australia's captain was at a restaurant on Wednesday night when a person at a nearby table to him discovered they had tested positive to the virus.

Cummins, who was dining with his brother and Adelaide Strikers player Harry Conway, immediately left the venue and notified officials.

The Australia quick has since tested negative for COVID-19, however, under South Australian health rules he must quarantine for seven days regardless.

Cummins' quarantine rules were confirmed just hours before the toss at the Adelaide Oval, promoting Steve Smith to captain Australia for the first time since the ball-tampering scandal in 2018.

Michael Neser will make his Test debut, as part of a new-look Australia attack with Jhye Richardson replacing the injured Josh Hazlewood.

"Gutted to miss this Test but really excited to see Neser finally get his chance in the baggy green," Cummins posted on Twitter.

"He has done the hard yards and is a seriously skilful player.

"Super frustrating but COVID has thrown us all some curve balls over the last couple of years. Will be cheering along!"

Incredibly, just a number of metres saved Australia from having their entire frontline bowling attack wiped out via the restaurant visit.

Both Mitchell Starc and Nathan Lyon were also present on Wednesday evening - as well as other Strikers players - but they were seated outside and therefore only deemed casual contacts.

Starc and Lyon were tested on Thursday morning, but both are free to play against England under SA health rules.

Cummins will be available for the Boxing Day Test, provided he continues to test negative.

There is no suggestion any party has done anything wrong, with incoming passengers into Adelaide from NSW and Victoria not required to quarantine after their initial test.

Regardless it means Travis Head will take up the role of vice-captain without Cummins in the side, after once holding the role in conjunction with the quick three years ago.

Cummins, the world's top-ranked Test bowler, claimed a five-wicket haul in the series-opening win at the Gabba and his absence comes as massive blow to Australia when considering Hazlewood's injury.

With Hazlewood unavailable, Cummins was expected to reclaim the new ball for the pink-ball match having taken 46 wickets at an average of 16.23 in day-night Tests.

Adelaide has had a rise in COVID-19 cases over the past week, with the 25 reported on Wednesday the most in a single day in more than 18 months.

Players are not in strict bubbles for the Adelaide Test, with both Australia and England players wanting as many freedoms as possible on the tour.

But the Cummins incident does call into question what protocols will be required for the next two Tests in Melbourne and Sydney, where case numbers are beyond 1000 per day.

Officials would also be desperate to avoid a repeat of the cancelled Test between England and India this year, after fears of an outbreak in the India camp.

India coach Ravi Shastri has since denied claims it was spread at the launch of his book in London, where he and others mingled with the public.

Australian Associated Press