Players and staff from both AFL clubs in Sydney plus NRL side the Sydney Roosters are undergoing COVID-19 tests after a known case visited venues through the city's eastern suburbs.
The Sydney Swans are awaiting results of tests conducted on Wednesday night.
Greater Western Sydney, who are slated to host Essendon at Giants Stadium on Saturday, also instructed players late on Wednesday to get tested.
Sydney Roosters players were on Thursday morning rushed in for tests, some 36 hours out from Friday night's NRL clash with Parramatta.
The main concern for the Swans and Roosters is a half-hour window at Azure Cafe on Monday, with the hot-spot venue in close proximity to both clubs' headquarters.
Swans coach John Longmire and some of his assistant coaches, who visited the cafe on Monday, are isolating as they wait for results.
The Moore Park cafe in the Entertainment Quarter is a popular coffee stop and lunch venue for NRL and AFL players, as well as other sports officials.
It's believed no Roosters were in the cafe at the same time as the confirmed case, while the Giants are also said to be confident that players have dodged the hotspots announced on Wednesday.
The NSW government announced on Thursday that masks would be compulsory indoors in Sydney for the next three days, also revealing the original case's wife has now tested positive for coronavirus.
Tests of other close contacts have all been negative so far.
The AFL, having only recently shifted this round's Fremantle-Brisbane match from Perth to Brisbane, is yet to indicate whether it is considering shifting the Giants-Bombers game to another venue.
It is possible that Longmire's team will fly out earlier than expected for Saturday's MCG clash with Melbourne, although that hinges on a range of factors.
The league's biggest worry, assuming the Swans and Giants all return negative tests, will be predicting the ease of interstate travel in and out of Sydney during coming weeks.
If coronavirus case numbers grow in the NSW capital then border closures could result in the Swans and Giants being forced to temporarily shift outside NSW.
Beyond Friday night's Roosters-Parramatta game, Magic Round also now shapes as a serious concern for the league given all NRL teams are due to to head to Brisbane next week.
Queensland and other states will be closely monitoring Sydney's COVID-19 numbers in coming days.
A-League club Sydney FC has been contacted for comment.