Travis Head, Australia's leading run-scorer in the ongoing Ashes, has been ruled out of the fourth Test here from January 5 after testing positive for COVID-19.
Head is asymptomatic and will remain in Melbourne with his partner for seven days as per the Victorian government's health requirements.
"As part of our testing procedures, we are PCR testing players, their families and our support staff daily," said a Cricket Australia spokesperson.
"Unfortunately, Travis returned a positive Covid-19 result earlier today. Thankfully, he is asymptomatic at this stage.
"We anticipate that he will be available to play in the fifth men's Ashes Test in Hobart."
The southpaw has scored 248 runs in the series at an average of 62 including a hundred in the series-opener at the Gabba.
The selectors have added Mitchell Marsh, Nic Maddinson and Josh Inglis to the squad as "additional cover".
A positive case in the Australian squad comes after a COVID outbreak in the England camp with head coach Chris Silverwood having to stay back in Melbourne after he was identified as a close contact of a person who tested positive for the virus.
Australia have already regained the Ashes by hammering England in the first three Tests.