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.
Neser suffered a side strain during Queensland's Marsh Cup defeat to New South Wales on Monday and the quick bowler will not travel for Australia's first tour of Pakistan since 1998.
His team-mate Steketee has been drafted into the squad for a three-match series that starts at Rawalpindi Cricket Stadium on March 4.
Steketee has taken 29 Sheffield Shield wickets at an average of 16.31 this season and claimed match figures of 8-100 against New South Wales last week.
Brendan Doggett is on standby to face Babar Azam's side along with Sean Abbott.
Jhye Richardson was not considered, as the Australia selectors manage his workload.
Morris, along with Queensland fast bowler Michael Neser, have been drafted into the 15-man Australia squad with doubts lingering over skipper Pat Cummins' availability due to a quad injury.
Cummins did not bowl in the second innings of Australia's 164-run win over the West Indies, which concluded on Sunday in Perth, but did spend time in the field and indicated he was hopeful of playing in Adelaide.
Victorian fast bowler Scott Boland, who was in Australia's initial 13-man squad, is Cummins' likely replacement should he not prove his fitness, with Morris and Neser coming in as cover.
Morris, 24, is a Test bolter, having enjoyed an excellent 2022-23 Sheffield Shield season for WA, taking a competition-high 27 wickets in five matches.
Neser, who made his Test debut against England in Adelaide last year, has taken 24 wickets in five Shield matches for Queensland.
"Michael has been with the squad on a regular basis in past seasons and was simply outstanding in Adelaide last summer," Australia selection chair George Bailey said. "He has continued to perform incredibly consistently since and will be warmly welcomed back.
"Lance is another of the outstanding young fast bowlers coming through the ranks. He has genuine pace and his ability to create opportunities for wickets is a real drawcard. It will be great experience for him to come into the environment."
Hosein took three wickets and scored a quick-fire 30 for Melbourne after Russell had bludgeoned them back into contention after a Michael Neser’s hat-trick had threatened to deny them victory.
Brisbane won the toss and chose to bat first but were two wickets down for 14 in the third over thanks to Mujeeb ur Rahman and Hosein who claimed the wickets of Max Bryant for five and Colin Munro for eight, respectively.
However, knocks of 25 from Sam Billings, 29 from Matt Renshaw and an unbeaten Jimmy Peirson helped stage a recovery. However, after a partnership of 61 between Billings and Renshaw both were dismissed by Tom Rogers in the 11th over as Brisbane slipped to 78-4.
It was soon 96-5 as Rogers dismissed Ross Whitely for 8 in the 15 over.
Hosein took the wickets of Neser (3) and James Bazley (0) in three balls in the 15th over. Peirson smashed 45 from 30 balls with six fours to get Brisbane to a competitive 138-7.
Rogers ended with 4-23 while Hosein took 3-26 in another solid performance with the ball.
Melbourne’s relatively simple chase of just under seven runs an over, became extremely difficult when Neser ripped through the top order with just nine runs on the board.
He dismissed Sam Harper first ball and then Jake Fraser-McGurk from the final ball of the first over and then in his second dismissed Nic Maddinson for two and Johnathan Wells for a duck in consecutive balls of his second over to leave Melbourne facing defeat.
However, Russell and Aaron Finch staged a recovery would set the team firmly on the path to victory.
Russell hit two fours and six sixes and he and Finch put on 81 for the fifth wicket before he got out caught behind off Mark Steketee for 57 from 42 balls.
Hosein picked up from where Russell left off hitting two fours and two sixes in a 39-run partnership with Finch. He eventually holed out to deep midwicket for 30 from 19 balls off the fifth ball of Steketee’s final over with Melbourne needing just nine from seven balls.
Will Sutherland smashed Steketee’s last ball for a massive six over the midwicket boundary leaving Finch to hit the winning runs, a four over extra cover to seal with victory from Bazley’s second ball of the final over.
Melbourne’s third straight win means they have six points and only trail leaders Adelaide Strikers on net run rate.
