Following the news that England head coach Chris Silverwood tested positive for COVID-19, Australian batsman Travis Head has also returned a positive result.
While the rest of the squads move on to Sydney for the fourth Test - scheduled to start on January 4 - Head will now stay in a mandatory seven-day isolation in Melbourne.
Head's result came back after the latest round of PCR testing, and with an outbreak in the England camp also, there's a growing doubt over whether the last two Tests will take place.
Match referee David Boon has also been forced to stand down from the New Year Test after contracting the virus, and the onward march of the Omicron variant has also threatened the continuation of the Big Bash League.
There appears to be a shared will from both sides to complete the full series as scheduled, despite Australia having already sealed a 3-0 lead.
The hosts began covering their bases by drafting in Mitchell Marsh, Josh Inglis and Nic Maddinson in as squad cover, yet even the act of calling up three players suggests they are already preparing for further absentees.
England's backroom team is already stretched thin, with spin coach Jeetan Patel, fast bowling specialist Jon Lewis and strength and conditioning lead Darren Veness all joining Silverwood in quarantine.
Should more players - from either side - start to be drawn in, there will be inevitable speculation over the viability of the series.
A Cricket Australia spokesperson has commented on the situation, saying, "As part of our testing procedures, we are PCR testing players, their families and our support staff daily.
"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 Vodafone men's Ashes Test in Hobart.
"We are grateful to our exceptional medical staff for all the work they have done throughout this series and we will continue to work with and support the players, their families and staff from both teams."
Head has averaged 62 this series, making him Australia's leading run-scorer with 248. He could be replaced by Usman Khawaja at the SCG, with the experienced batter having served 12th man duties throughout the series.