"The team member was tested and self-isolated as soon as they started to show symptoms and will now be treated by local healthcare authorities," McLaren said in a statement
McLaren pulled out of the season-opening Australian Grand Prix Thursday after a team member tested positive for coronavirus, throwing the race into chaos.
The employee was among at least five Formula One personnel -- four from Haas -- who went into isolation this week after showing flu-like symptoms typical of the virus.
"The team member was tested and self-isolated as soon as they started to show symptoms and will now be treated by local healthcare authorities," McLaren said in a statement, adding that he would be quarantined.
"The decision (to withdraw) has been taken based on a duty of care not only to McLaren F1 employees and partners, but also to the team's competitors, Formula 1 fans and wider F1 stakeholders."
Results of the tests for the Haas staff have yet to be revealed.
McLaren Racing withdraws from the 2020 Formula 1 Australian Grand Prix. pic.twitter.com/BZvHVKQoev— McLaren (@McLarenF1) March 12, 2020
McLaren's decision to pull out casts doubt over whether the race will be run without a full complement of teams, and whether others will follow suit.
World champion Lewis Hamilton earlier Thursday said he was "very surprised" that it was going ahead as fears mount about the spread of the disease.
"I am really very, very surprised that we're here. I don't think it's great that we have races but it really is shocking that we're all sitting in this room," he said at an official pre-race press conference packed with media.
"It seems that the rest of the world is already reacting a little bit late, but you have seen this morning with (President Donald) Trump shutting down the border to Europe to the States, the NBA suspended, yet Formula One continues to go on.
"It's a concern I think for the people here. It's quite a big circus that's come here, it's definitely concerning for me."
The Mercedes star, who is gunning to match Michael Schumacher's record seven world crowns this season, sat alongside Ferrari's Sebastian Vettel and Renault's Daniel Ricciardo in the media session, but a large open space separated them from the press.
Asked why he felt the race was still on, Hamilton replied: "Cash is king."
Four-time world champion Vettel said it was difficult to judge what to do as the virus continues its spread.
"Obviously we have to trust the FIA (International Automobile Federation) to take precautions as much as they can, but I think the answer that nobody can give you at the moment is how much you can control what is going on," he said.
"As a matter of fact, we are here so you just try to take care as much as you can."
Haas team principal Guenther Steiner said they had not yet discussed what to do if any of their employees tested positive.
"We'll cross that bridge when we get to it," he said.
Australia has reported 150 cases of coronavirus so far, including among fans who attended the women's T20 Cricket World Cup final and a Super Rugby match, both in Melbourne last week.
European countries that are home to many of the F1 teams and journalists at the grand prix have had far more cases.
BREAKING: Formula One organisers are staring down the last-minute cancellation of this weekend’s season-opening race after McLaren withdrew due to a coronavirus diagnosis.https://t.co/uXH7KpljtG— 7Sport (@7Sport) March 12, 2020
Despite concerns, fans flocked to Albert Park on Thursday for a Supercars qualifying session.
"I'm not worried, I'm washing my hands and that's the best thing to do," said spectator Robert Clarke as he used a hand-sanitiser station.
The first F1 practice sessions are due to start on Friday.
In an attempt to limit interaction between drivers and fans, autograph sessions have been replaced by question and answer interviews, with selfies banned.
Media events have also been hit with Renault's Ricciardo and Esteban Ocon "excused" from a press conference Wednesday, and an exclusion zone was enforced around Max Verstappen and Alex Albon at a Red Bull function.
Ocon was spotted wearing a mask in the paddock on Thursday, while teams scrapped all-in TV interviews, where media are tightly packed around the drivers, for the duration of the weekend.
The coronavirus has already hurt the sport with April's Chinese Grand Prix postponed, while the second race of the year in Bahrain will be held without spectators.
McLaren withdraw from the Australian Grand Prix after a team member contracts coronavirushttps://t.co/DCckpvJQA0— Formula 1 (@F1) March 12, 2020
The Australian Grand Prix Corporation said it was working closely with health authorities to take additional precautions at Albert Park, including having hand sanitisers at public areas and corporate facilities.
Cleaning and disinfection programmes have been increased and protocols implemented to respond to any suspected COVID-19 cases.
Over the weekend, the FIA said it was establishing a "crisis cell" to meet every two days to monitor the global threat posed by the virus.