Brisbane Lions player Matt Maguire retired this week after the seventh concussion of his career, in a NEAFL game on Anzac Day, with the 31-year-old still unable to train at a high intensity without suffering headaches and blurred vision almost two months later.

Leading AFL doctor Peter Larkins said there was little indication of what caused long-term symptoms of concussion and a higher impact didn't necessarily mean worse concussion.

"There are very low-grade concussions that result in long-term symptoms and very high grade concussions where the symptoms resolve really quickly so there's no magic number," he said.

"It's not like three is the magic number or four but you try to avoid any because it's better to have none and two in one season's worse than one in one season.

"We're still accumulating knowledge but less is better, there's no doubt."

The lack of certainty around prevention of concussion, aside from avoiding contact, makes the issue tricky but Dr Larkins said the progress made recently in the AFL, including contacting and testing former players and taking players off after head knocks , was a good start.

"You don't want to change the fabric of the game," he said.

"It's very hard as a doctor to say well we've got to improve safety in the game by not allowing them to put their head over the ball or punch the ball when they're in the air," he said.

Helmets and headgear prevent superficial head injuries but Dr Larkins said there was no evidence to suggest they had a positive influence on concussion rates.

The duty of care of players has been dragged into the spotlight after Carltons' Bryce Gibbs was handed a two-week suspension for a sling tackle that left Port Adelaide's Robbie Gray concussed.

Dr Larkins said the sling tackle should go the way of the rugby codes' spear tackle, though it is not as risky a technique.

Maguire said he understood both sides of the concussion debate.

"I think concussion is a by-product of a contact sport," he said.

"I am in favour of doing everything we can do to reduce the occurrences of concussions and head-high hits because it is a problem.

"But there's a fine line between ruling it out completely and also trying to keep the aggression and all the things that make our game great."

Maguire is the second Brisbane Lion in as many seasons to retire due to concussion, following former captain Jonathan Brown.

The football future of North Melbourne's Leigh Adams is also in doubt after he suffered another serious concussion in the VFL.