Australia moved within tantalising reach of retaining the Ashes in Melbourne on Monday but the fate of the series may be decided in a laboratory rather than on the field after the England camp was hit by a rash of Covid-19 cases.
Two England support staff and two of their family members were in isolation after testing positive for Covid-19, throwing a scare through the team as they prepared to head to the Melbourne Cricket Ground for day two of the third test.
The players were all cleared after rapid antigen tests and play proceeded without disruption barring a half-hour delay.
However, England will need to wait for the results from more thorough PCR tests to be clear to return for day three on Tuesday, which they do not expect to receive until morning.
Under ICC rules, teams are allowed to make replacements for players ruled out by Covid-19 with the match referee's approval, so long as the substitutes are considered "like-for-like" and would not provide undue advantage.
An England team spokesman said it was still to be decided how the match would proceed if there was a positive Covid-19 case among the players.
It was also unclear whether players would be deemed close contacts of any infected team mates and be forced to isolate.
"We're all having PCR tests now," England paceman James Anderson told reporters.
"And obviously, we need all those to be clear, really, if possible, so we'll just have to wait and see what the results are."
The Covid tension added to a deflating final session on Monday for England, who were staring down the barrel of another heavy defeat following losses in Brisbane and Adelaide.
They were 31 for four in their second innings at stumps, still needing 51 runs to make Australia bat again.
Trailing 2-0 in the series, Joe Root's side need to win in Melbourne to keep the series alive.
While the odds are stacked against them, having the match called off would be a bitter pill to swallow.
Even with two tests to play in Sydney and Hobart, holders Australia would, by default, retain the urn if Melbourne is unable to proceed or be rescheduled.
That could also place the rest of the series under a cloud.
England's players were already reluctant to tour Australia under strict Covid protocols and that reticence may only grow with the Ashes lost and nothing left to play for.
With a large amount of revenue at stake, host board Cricket Australia (CA) is naturally desperate to see the series play out as scheduled.
CA boss Nick Hockley rejected any need for alterations to the schedule or to shift the fourth test to Melbourne from Sydney, where authorities are battling a steep rise in Covid cases.
"We've got great confidence in the protocols," he told reporters at the MCG.
"This is something that we're all having to live with."
Covid has already proved a disruption in the series, if not impacting Australia's dominance.
Home captain Cummins was forced to miss the second test in Adelaide and isolate for a week after being identified as a close contact of a case.
Australia shrugged off his absence to win by 275 runs.