The mystery of Conor McKenna’s positive coronavirus tests may never be solved, AFL chief executive Gillon McLachlan says.

Essendon’s McKenna returned positive results to COVID-19 from tests last Friday and Saturday, prompting the AFL to postpone the Bombers’ scheduled match against Melbourne.

The Irishman has twice tested negative since, though he remains in 14-day self-isolation.

McKenna’s teammate James Stewart, deemed a close contact of the Irishman, also remains in self-isolation.

McLachlan says how McKenna was infected may never be known.

“There is chance that it was from some time ago and there is some level of remnants in his system at very low levels,” McLachlan told 3AW radio on Friday.

“We will do further blood testing and blood work.

“But he definitely was positive … whether it was from an illness in Ireland or other, that is for the medical people to continue to work through.

“And maybe we won’t have certainty on it.”

McKenna spent 14 days in isolation on return to Australia from Ireland during the AFL’s suspension of competition amid the coronavirus pandemic.

He was understood to have attended open-house inspections in the period leading up to his positive test.

McLachlan said the AFL would meet on Friday to determine if McKenna breached any of the code’s coronavirus protocols.

“There’s wild theories … going around,” he said.

“It’s accepted that he went to some public real estate openings and to his host family.

“Both of those breaches are marginal.”

The AFL has previously suspended Melbourne pair Charlie Spargo (two games) and Kysaiah Pickett (one game), and Port Adelaide’s Ollie Wines (one game) and Essendon’s Brandon Zerk-Thatcher, for breaching the code’s virus protocols.