Six Australian Open warm-up events were on hold and hundreds of players and officials in isolation on Thursday as a fresh coronavirus case left organisers scrambling to ensure the Grand Slam tennis tournament goes ahead.
Health officials insisted the risk to players and officials was "low" after a worker at one of the tournament's designated quarantine hotels tested positive.
But Thursday's play at six tournaments at Melbourne Park - five ATP and WTA warm-up tournaments, as well as the ATP Cup team event - was cancelled as a precaution.
The season's first Grand Slam, starting on Monday, has already had a rocky build-up after it was delayed three weeks to allow players to quarantine and get match-fit in the warm-up events.
Victoria state Health Minister Martin Foley said the 520 people ordered to isolate and get tested were casual contacts, stressing "we are not as concerned about them".
"But out of an abundance of caution we want to ensure we leave no stone unturned in how we follow up and deal with anybody who may have had contact with this individual," he said.
Dedicated facilities have been set up to ensure they all get tested quickly and can potentially be back on court by Friday, with results often returned within 24 hours.
Victoria's Deputy Chief Health Officer Allen Cheng concurred that the risk to them was "relatively low".
Stefanos Tsitsipas and Stan Wawrinka were reportedly among those affected although the biggest names of the game, including Serena Williams, Novak Djokovic and Rafael Nadal, will not be among them as they spent their mandatory 14-day quarantine in Adelaide.
More than 1 000 players, coaches and officials flew into largely virus-free Australia last month, sparking debate over the whether the tournament should be held during a coronavirus pandemic.
The latest difficulties highlight the problems currently associated with holding large-scale sporting events with less than six months to go until the Tokyo Olympics.
Aggressive restrictions on incoming travel have meant Australia has been one of the world's most successful countries in dealing with the pandemic and one of the few still able to have spectators at sports events.
Daily crowds of between 25 000 and 30 000 are expected at the Australian Open.
Victoria Premier Daniel Andrews said while there was "no guarantees" he did not expect the scheduled start of the Grand Slam to be affected, although state opposition leader Michael O'Brien demanded a definitive call within 48 hours.
"We don't want to see a situation as we did with the Grand Prix, where crowds were literally turning up, only to be turned away," the Melbourne Herald Sun quoted O'Brien as saying.
"I think people are entitled to know what's happening, and the government should be making their minds up in the next 24 to 48 hours."
Last year's Formula One Grand Prix in Melbourne, the traditional season curtain-raiser, was cancelled just hours before the first practice session after a McLaren team member tested positive.
The late decision left fans fuming as they queued to get in.
The draw for the Australian Open is due to take place later Thursday and while resentment has been bubbling on social media over whether the tournament should go ahead, on the quiet streets near Melbourne Park the public gave a mixed response.
"I'm just disappointed because the Australian Open seemed from the beginning about profits and not the safety of the public," said John Reilly, echoing some of the online sentiment.
But local resident Greg Rodgers said the two-week spectacle represented a "return to normalcy".
"The Australian Open is special, especially if you live in the area, because it brings such a positive impact to the city and industries," he said.
Victoria had gone 28 days without a locally acquired infection before the latest case, which prompted a tightening of restrictions around wearing masks.
State authorities are extremely wary of coronavirus cases after Melbourne spent four months in lockdown until late October.