TOPSHOT - The sun sets during the first innings of the day-night third Test cricket match between Australia and South Africa at the Adelaide Oval in Adelaide on November 24, 2016. / AFP / Peter PARKS / IMAGE RESTRICTED TO EDITORIAL USE - STRICTLY NO COMMERCIAL USE (Photo credit should read PETER PARKS/AFP/Getty Images)

Cricket Australia could be forced to cancel their second Big Bash League game in as many days with a Sydney Thunder player reportedly testing positive to COVID.

While new national rules regarding what defines a close contact were brought in overnight by prime minister Scott Morrison and the national cabinet, South Australia's public health rules regarding a close contact haven't changed as yet.

Under the new national rules, four hours is the minimum time someone would have to spend with a positive case to be deemed a close contact.

In South Australia that rule is still set at 15 minutes, meaning the entire Sydney Thunder squad could be deemed close contacts and forced into isolation in much the same way Pat Cummins was ahead of the second Ashes Test in the city earlier in December.

Cricket Australia are currently scrambling to work out if tonight's game can go ahead, according to a Fox Sports report, who broke the news on Friday morning.

The Thunder squad have all had PCR tests and are expecting their results back in the early afternoon, but even if all come back negative, there is reported to be substantial doubt over the game proceeding.

The differences in rules between cities are proving a major headache for Cricket Australia, with the Ashes recently allowed to proceed in Melbourne despite four positive cases (which has now blown out to seven) on the same day in the English camp ahead of Day 2 in the Boxing Day Test.

It's understood the Strikers are not impacted.

The positive test comes after last night's Melbourne Stars and Perth Scorchers clash was called off over COVID, with a positive case in the Stars' staff leaving no time for PCR tests to be completed on players prior to the first ball.