McGrath, who has helped turn Australia’s year-opening Test into a fundraising drive to support those with breast cancer, is hopeful that will return a negative test in time to attend day three of the SCG Test, now known as Jane McGrath Day.
The former paceman will have a virtual presence at the ground on Monday when both sides are given their baggy pink caps.
“Glenn has had a PCR test which unfortunately returned a positive result,” McGrath Foundation chief executive Holly Masters said.
“We wish Glenn and his family good health.
“We are grateful to our partners at Cricket Australia and the SCG.
“As well as the England cricket team and the broadcasters for their ongoing support for the Pink Test and look forward to still making this the ‘pinkest’ Ashes.”
Ashes schedule of the remaining matches:
Fourth Test: January 5-9, SCG
Fifth Test: January 14-18, Blundstone Arena