Between 500 and 600 players, officials and staff for the Australian Open will be forced to isolate after a worker at one of the event's quarantine hotels tested positive for coronavirus.
The Australian Open is due to get underway in Melbourne on Monday and had been pushed back by three weeks in order to give players time to quarantine on arrival to Australia.
A worker at one of the tournament's quarantine hotels returned a positive test, which has led to the reintroduction of restrictions across Victoria from midnight.
The 26-year-old man had been working as a resident support officer as part of the Australian Open quarantine program.
Up to 600 people associated with the first Grand Slam of the year have been identified as casual contacts and made to self-isolate until they receive a negative test.
Victoria Premier Daniel Andrews announced in an emergency press conference on Wednesday that it may have an impact on Thursday's play at events in the lead-up to the Australian Open.
"This is one case. There's no need for people to panic," he said.
"There's no need for people to be alarmed. We Victorians know what to do, and we have proven, as a state, very successful at managing these sorts of outbreaks, these sorts of issues."
"We have one case and the decision has been made, the event will proceed next week."
"We can't particularly determine how it is the person became infected given that they produced negative test results.
"All of that will become clearer with a combination of CCTV footage, genomic sequencing, further testing, all of that coronavirus detective work that already well and truly underway.
"We are continuing to talk to him tonight to extract as much information as possible about his movements."
More than 1,000 people, players and members of their teams were obliged to undergo 14 days of quarantine on arrival to Australia.
The Australian Open will be allowed to admit up to 30,000 fans a day, around 50% of the usual attendance, when the Grand Slam gets underway on Monday, February 8th.