The Melbourne Cricket Ground and AAMI Park have had their exposure site statuses expanded over fears of more "stranger-to-stranger" COVID-19 cases.
Two of Victoria's 13 new local cases reported in the 24 hours to Monday morning were linked to the major sports stadiums.
One involves a Mildura man who attended the AFL clash between Carlton and Geelong at the MCG on July 10.
He was on the margins of the already listed exposure site sections on level two in the members' reserve, where an unknowingly infected Ariele Apartments resident had been seated.
It has prompted authorities to list another two sections - 40 and 46 - as tier-two exposure sites and ask contacts within the five other affected bays to get retested as a precaution.
"We cannot make the whole of the MCG a tier-one site," Chief Health Officer Brett Sutton told reporters.
"Quarantining tens of thousands of people and overwhelming testing with tens of thousands of people, that would be an overreach."
The other new case was in the stands at AAMI Park for the Australia-France international rugby clash on July 13.
Professor Sutton suspects the spectator caught the virus from the initial case at an entry "pinch point", given neither were seated anywhere near each other.
As such, sections 81 to 91 of the rectangular stadium have been added as tier-two sites, and patrons must get tested and isolate until they receive a negative result.
Other sections of AAMI Park remain classed as tier-one exposure sites.
With more instances of "stranger-to-stranger" transmission, Prof Sutton is unsure whether Victoria will be able to return to the 75 per cent outdoor capacity crowd limit in place prior to the state's fifth lockdown.
He said public health officials were assessing other risk mitigation techniques for major sports crowds including harder sub-zones, staggered entry, rapid pre-event antigen testing and checking fans' vaccination status.
"I've always said that needs to be a national consideration. We shouldn't be going out alone on that," Prof Sutton said.
"But all of those things should be in play."
Premier Daniel Andrews would not be drawn on if the current outbreak of the more infectious Delta variant would force the AFL grand final to move from the MCG for a second straight year.
"It's far too early to be speculating about those things," he said.