The Victorian government has clarified tennis fans will be required to wear a mask when the roof is closed on the main arenas during the Australian Open.
The ruling is in line with restriction changes on Wednesday, following Melbourne's Grand Hyatt virus case.
It applies to the main courts of Rod Laver Arena, Margaret Court Arena and John Cain Arena, where the biggest stars in world tennis will feature in the first grand slam of the year.
"These venues are deemed to be indoor spaces under the restrictions and masks use is required by all spectators and officials," a government spokesman said.
Spectators can remove masks when the roof is open, while players are exempt from the rule.
All 507 players, officials and support staff have returned negative COVID-19 results after undergoing further testing following the hotel quarantine worker case.
The results paved the way for the Australian Open to go ahead as planned from Monday.
"We're pleased that everyone tested negative," said Tennis Australia boss Craig Tiley, the tournament director.
"The past few days haven't been easy for anyone and I'm incredibly proud of the players and our staff.
"Many of us have had sleepless nights, but that's just how it goes."