Victoria has recorded no new local or interstate coronavirus cases for a ninth day in a row, as the state government defends its border restrictions with Greater Sydney.
The state reported zero local cases and two new cases among international travellers in hotel quarantine on Friday from more than 15,000 tests.
However, the Department of Health and Human Services received notification of a very low positive result on Thursday.
"That person has had multiple tests over the last 24 hours, all of which have been subsequently returned negative," Health Minister Martin Foley told reporters on Friday.
He said it was likely the case was either a false positive or persistent shedding from a historic infection.
The person will remain in isolation until they receive the results of further tests.
They are not linked to a known case or public exposure site.
It comes as Mr Foley defended the state's border restrictions with Greater Sydney.
While the state reopened its border to regional NSW on Monday, thousands of Victorians have been stranded in Greater Sydney for more than two weeks as it is classified as a "red" zone.
Greater Brisbane, which emerged from a three-day lockdown earlier this week, also remains a red zone.
Mr Foley said the government is constantly reviewing the red zones, taking into account the number of active cases and mystery cases in both states.
"Let's be clear, there's almost 200 cases circulating in the Greater Sydney community since December the 16th, not just on the northern beaches," Mr Foley said.
"We're more than confident that our colleagues in New South Wales are mopping this up, but there have been chains of unknown transmission for many weeks now in Sydney."
Mr Foley said the restrictions would change when the risk lowered.
"I understand the frustrations and the dislocation this is causing but even more so I understand the frustration and dislocation that another cluster outbreak in Victoria would cause," he said.
Some 128,833 permit applications have been approved since the state's new permit system came into effect on Monday, including 20,841 in the last 24 hours.
A total of 1886 exemptions for those in red zones have also been processed.
Premier Daniel Andrews Andrews on Thursday said the government was looking to reduce the red zone in Sydney to local government areas, but did not set a time frame.
As thousands of Victorians remain stranded interstate and overseas, more international tennis stars arrived in Melbourne on Friday ahead of the Australian Open on February 8.
All players will undergo 14 days of quarantine at one of three Melbourne hotels and will be tested for COVID-19 daily.
Mr Foley confirmed two players - former world No.1 Andy Murray and American Madison Keys - were unable to travel to Australia after returning positive COVID-19 tests.
World No.50 Tennys Sandgren, however, was allowed on a chartered flight after also returning a positive test.
The American tweeted he was not contagious and had "totally recovered" from the virus after first testing positive in November.
Mr Foley said Sandgren's positive test was reviewed by health authorities and determined to be viral shedding.
In regards to Murray, the health minister said the crowd favourite would not be receiving any special favours.
"Mr Murray and the other 1240 people as part of the program, need to demonstrate that if they're coming to Melbourne they have returned a negative test," he said.
"So should Mr Murray arrive, and I have no indication that he will, he will be subject to those same rigorous arrangements as everyone else."
Australian Associated Press