Melbourne United NBL players Mitch McCarron and Jo Lual-Acui have tested positive for COVID-19.
Training for Victoria's NBL teams, United and South East Melbourne, has been suspended immediately.
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McCarron and Lual-Acui were tested and isolated as soon as they started displaying symptoms.
All United players and staff who attended training on, or after, July 22 will be tested for coronavirus.
Even if the players and staff return a negative test, they will still need to self-isolate for 14 days.
United had been training at the Melbourne Sports and Aquatic Centre.
NBL commissioner Jeremy Loeliger said the league was providing support to the two Melbourne clubs and affected players.
"Our concern is for players and staff and ensuring that we follow the right protocols to minimise any further risk to the wider community," he said.
"We have decided it's in the best interests to also suspend South East Melbourne training as a precautionary measure.
One of the big fears is how insulated the Melbourne basketball community is; guys are working out with each other all the time, and some share gyms, trainers, physios, etc. Players who went to Boomers workouts might have also gone to training sessions with NBL teams.— Olgun Uluc (@OlgunUluc) July 29, 2020
"Given the current situation in Melbourne, we do not want to take any risks and we will continue to work with the relevant health authorities to ensure all protocols are followed."
McCarron, a shooting guard, has played for United since 2018 after a stint with Cairns.
Towering centre Lual-Acui joined United last year.
NBL spooners add American shaprshooter
The Illawarra Hawks have taken another big step in their fresh NBL start under master coach Brian Goorjian, signing American sharpshooter Tyler Harvey as the first import on their 2020-21 roster.
Harvey, whose trademark is his three-point shooting, joins fellow recruit Deng Adel on a new-look team after the former Cleveland Cavaliers forward committed to the Wollongong-based club last week.
The 27-year-old Harvey has played professionally in Germany, France, Italy and America's G-League, where he scored 58 points in a game for Memphis Hustle in February last year.
"Tyler's scoring and shooting attributes are well known across the world and we believe he can make an instant impact in those areas for us," Goorjian said.
"He will play a key role for the Hawks this season as we construct a team that the fanbase can be proud of on and off the court."
Harvey was a prolific scorer in three college seasons with Eastern Washington and was the 51st overall pick in the 2015 NBA draft, selected by Orlando Magic.