Up to 600 players and support staff connected to the Australian Open will have to isolate until they have been tested for COVID-19 after a hotel quarantine worker in Melbourne returned a positive result for the virus on Wednesday.
Play at the six warm-up events for the Grand Slam at Melbourne Park is likely to be heavily disrupted on Thursday but Victoria Premier Daniel Andrews said it should not impact the Australian Open itself, which starts on Monday.
"There is a number of about 500, 600 people who are players and officials and others who are casual contacts," Andrews said at a news conference late on Wednesday.
"They will be isolating until they get a negative test and that work will be done tomorrow."
Victoria, of which Melbourne is the capital, reintroduced the compulsory wearing of masks in indoor public places from Thursday while private gatherings were reduced from 30 people to 15.
About 1,200 players, coaching staff and officials arrived in Australia at the middle of last month for the year's first Grand Slam and went into a mandatory 14-day isolation.
The players were allowed five hours outside for training but 72 of them were confined to hotel rooms for the two weeks after passengers on three charter flights taking them to Australia tested positive to the novel coronavirus.
Participants of the Australian Open were given the green light to begin exiting COVID-19 quarantine from end of last week with most of them involved at the ATP, WTA events at the site of the hardcourt major.
COVID-19 Quarantine Victoria (CQV) said in a statement that a man, who worked his last shift at the Grand Hyatt Hotel in Melbourne on Friday, returned a positive result on Wednesday.
"We are contacting all Australian Open players, officials and support staff who were staying at the Grand Hyatt during the entire period," said CQV, the government agency overseeing the quarantine of participants ahead of the Grand Slam.
Australian Nick Kyrgios, who defeated Harry Bourchier on Wednesday to reach the last 16 of the Murray River Open tuneup, asked on Twitter: "Am I playing tomorrow?"
Tennis Australia, who are the organisers of the Febuary 8-21 Grand Slam, did not immediately respond to request for comment.
"At this stage there is no impact on the tournament proper," Andrews added. "I must say [the Australian Open] is important to us but the issues are much broader and that is about public health and public safety.
"This is one case. There's no need for people to panic. There's no need for people to be alarmed."