MELBOURNE (AP) — Some players preparing for the Australian Open will have to isolate until they return a negative test for COVID-19 after a worker at one of the tournament’s quarantine hotels tested positive for the virus.

Daniel Andrews, the political leader of Victoria state, called a late-night news conference Wednesday to announce the case and urged anyone with symptoms in Melbourne to get tested.

Andrews said the case could have an impact on some of the six tuneup tournaments being held this week ahead of the Australian Open, with any players, coaches or officials who quarantined at the Grand Hyatt hotel in Melbourne deemed to be casual contacts of the 26-year-old infected man and required to isolate until they’ve returned a negative test.

The hotel advertises it has 550 rooms, including 25 premium suites, so potentially hundreds of people could be involved. It could also test the resolve of players who have recently come out of two weeks in quarantine, and give ammunition to critics of the decision to allow people to fly in from all over the world for the Australian Open.

“It may have an effect on tomorrow’s play in the leadup event,” Andrews said. “At this stage, no impact on the tournament proper.”

The Australian Open is scheduled to start Monday, with up to 30,000 spectators expected daily at Melbourne Park under guidelines which allow for up to 50% capacity.

Australian Open organizers didn’t immediately have details of how many players would have to isolate.

Everyone who arrives in Australia must undergo a mandatory 14-day quarantine under the COVID-19 pandemic regulations. The Australian Open used three hotels in Melbourne for the bulk of the players to quarantine and had other secure accommodation and facilities in Adelaide, South Australia state, for some of the biggest stars, including Serena Williams, Naomi Osaka, Novak Djokovic and Rafael Nadal.

The infected worker tested negative on his last day at the hotel on Jan. 29 but subsequently tested positive and has been working with government and health officials on contact tracing.

“This is one case,” Andrews said. “We’re well trained and well schooled in what to do.”

He said he was holding the news conference and announcing restrictions, which require the mandatory use of face masks while indoors, “through an abundance of caution.”

SERENA ADVANCES

Hours before the government’s announcement, 23-time major champion Serena Williams beat Tsvetana Pironkova 6-1, 6-4 to advance to the quarterfinals of the Yarra River Classic.

She will next face Danielle Collins, who upset third-seeded Karolina Pliskova 7-6 (5), 7-6 (3), and could reach a semifinal match against top-ranked Ash Barty.

Williams was later asked when was the last time she played a warmup tournament so close to a major.

The U.S. Open, last year, was her short answer. Then she elaborated.

“But before that, before this whole pandemic, I could count the times on one finger I’ve done that,” she said. “I’m just happy to be out here in any circumstances. It’s so cool after what the world went through the last 12 months.”

Williams had a tough win over Pironkova in last year’s U.S. Open quarterfinals, and then withdrew from their scheduled second-round match at the French Open because of an Achilles injury.

Williams won her last major title at the 2017 Australian Open, when she was pregnant with her daughter, Olympia. She’s still chasing Margaret Court’s all-time record of 24 Grand Slam singles titles, and an eighth in Australia.

Barty, aiming to break a long drought for Australian women at the national championship, had a 6-0, 4-6, 6-3 win over No. 52-ranked Marie Bouzkova and will next play Shelby Rogers.

On the bottom half of the draw, defending Australian Open champion Sofia Kenin rallied from a set and a break down to fend off Jessica Pegula 5-7, 7-5, 6-2.

ATP CUP

Italy and Russia were the first teams to reach semifinals of the ATP Cup, the 12-team men’s event.

Fabio Fognini beat Benoit Paire before Matteo Berrettini defeated Gael Monfils 6-4, 6-2 to clinch Italy’s win over France, giving the Italians top spot in Group C.

Daniil Medvedev secured Russia’s win over Japan when he beat Kei Nishikori 6-2, 6-4. Russia is on top of Group D with wins over Argentina and Japan.

“Really happy for the team,” Medvedev said. “Semifinals is a big step … hopefully we can go further than that.”

In Wednesday’s other matches, Germany opened with a win over Canada, with Jan-Lennard Struff downing Milos Raonic 7-6 (4), 7-6 (2) and Alexander Zverev holding off Denis Shapovalov 6-7 (5), 6-3, 7-6 (4).

Canada was coming off an opening loss to defending champion Serbia. Germany will play Serbia for first place in Group A on Thursday.

OSAKA IN THREE

U.S. Open champion Naomi Osaka advanced in the Gippsland Trophy, but needed three sets after a slow start.

Osaka had a first-round bye and dropped only four games en route to her second-round win, so a 3-6, 6-3, 6-1 win over No. 371-ranked Katie Boulter was a change of pace. Next up for her will be Irina Begu, who upset fifth-seeded Johanna Konta 4-6, 7-6 (10), 7-6 (4).

Second-ranked Simona Halep had a more straight-forward 6-2, 6-4 win over Laura Siegemund.

Also advancing were third-seeded Elina Svitolina, who beat former French Open champion Jelena Ostapenko 6-7 (4), 6-3, 6-2, and No. 7 Elise Mertens.

CHAMPIONS IN GRAMPIANS

Three-time major champion Angelique Kerber took a while to adjust in her first match since leaving quarantine, beating Katerina Siniakova 6-3, 4-6, 6-3 in the Grampians Trophy tournament.

It’s the event for those players who were forced into hard lockdown — not allowed to leave their rooms, even for practice — after being deemed close contacts of passengers on their flights who test positive for COVID-19 after arriving in Australia.

Other major champions in the draw include Sloane Stephens and Svetlana Kuznetsova, who both lost in the first round. Two-time Australian Open champion Victoria Azarenka had a first-round bye.

Reporting by John Pye/AP; contributing Dennis Passa in Brisbane, Australia. Trademark and Copyright 2021 The Associated Press. All rights reserved.