Melbourne's two NBL clubs have suspended training after United players Mitch McCarron and Jo Lual-Acui tested positive for COVID-19.
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, while cross-town rival South East Melbourne Phoenix are based about 40 km away in Wantirna South.
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.
"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 who has been a member of the Australian Boomers squad, has played for United since 2018 after a two-year stint with Cairns.
Towering centre Lual-Acui joined United last year.
Melbourne United chief executive Vince Crivelli said McCarron and Lual-Acui were in a "little bit of shock".
"Both Mitch McCarron and Jo Lual-Acui are working with the relevant departments and the contact tracing starts," he told SEN.
"Like anyone they certainly didn't feel too bad but notwithstanding they've got a positive test and now we just deal with it."
Australian Associated Press