Australian captain Pat Cummins has sensationally been ruled out of the second Ashes Test against England, deemed a close contact of a person who received a positive COVID-19 test.

The news comes on the morning of the first day of the pink-ball Test at Adelaide Oval, with Queensland fast bowler Michael Neser confirmed to replace Cummins in the XI for his debut on Thursday.

Former skipper Steve Smith will captain Australia in the absence of Cummins in the day-night Test in Adelaide.

Cummins was dining at a restaurant on Tuesday and was sat nearby to someone who has since been confirmed as a positive coronavirus case.

The star paceman did not breach any biosecurity protocols and isolated as soon as he became aware of the situation. Cummins has since had a PCR test, which produced a negative result.

However, Cummins has been confirmed as a close contact by South Australia Health and will be required to isolate for seven days, ruling him out of the second showdown with rivals England.

Cricket Australia (CA) said it anticipated Cummins will be available to play in the Boxing Day Test at the MCG in Melbourne.

"Cummins is understandably very disappointed not to be able to captain Australia for the day-night Test in Adelaide," CA said in a statement.

The 28-year-old fast bowler had led Australia to a nine-wicket victory in the Ashes opener as skipper in Brisbane, after taking over from Tim Paine.

Smith's deputising marks the first time he will have captained his country since the controversial 2018 sandpaper-gate Test match in Cape Town, which led to his dismissal as skipper and 12-month suspension.

Australia may have dodged a further bullet, revealing Mitchell Starc and Nathan Lyon were also dining at the same restaurant but at a separate table outdoors.

Both have been deemed casual contacts by SA Health and are free to play.