While he has gone into concussions protocols, it remains unclear why the Demons defender suddenly became unsteady on his feet and had to be helped from the MCG during the Brisbane clash.
"It's a unique situation. We're still doing some tests with him," coach Steven King said before Wednesday training.
"We're still not really sure exactly what's happened - we're exploring all those possibilities.
"We've put him in protocols at the moment, because that's the most obvious, but we're still not 100 per cent sure that's the case.
"There's still a range of things it could be."
Teammates rushed to support Petty, three days after the worrying circumstances around Carlton player Elijah Hollands.
As Carlton review how Holland was allowed to stay on the field for so long, there is talk of a mental health-themed game potentially involving the Demons and the Blues.
"After the week we've had, as an industry it's important we make moves to support and put the right things in place around people," King said.
Petty's mystery health problem means there will be at least one change for the annual Anzac Eve match this Friday night against Richmond at the MCG.
King expects selection will be tough, given the occasion.
"I don't think there will be too many players putting their hand up, saying "I want to miss this one'," he said.
The Demons are coming off an impressive win that left them 4-2, while the Tigers are winless. King said he heard off-season predictions that had his team would be in that sort of hole.
"Over summer, people were saying we were going to be 0-6. I didn't see that, from the way we were training," he said.
King added the experience of beating the reigning premiers last weekend would be invaluable for his young team.
"Some of those young players ... it would be worth 10 or 15 games worth of experience, just playing against that quality of team and players, in that type of game."
Second-year player Harvey Langford has been a standout so far and King said that is a reward for the extra work he is doing with assistant coach Nathan Jones.
"Footy is a pretty complex game, but it's pretty simple as well - the harder you work, the luckier you get," King said.
Also on Wednesday, Richmond announced Sam Cumming will become their fourth debutant this season in Friday's match.
The midfielder was the Tigers' top pick in the draft last November, taken at No.7. His performance in a practice match last week against the Australian under-18 academy helped seal his senior selection.
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