Colin Scotts has suffered thousands of head knocks over his football career, but he can recall the worst - the dizziness morphed into pain, blocking his ability to absorb and answer basic questions such as where he was.

His brain had "shut off", but his team encouraged him to get back onto the field, not realising that what he desperately needed was time to rest and heal.

"After our professional football careers, yes, there are issues with obesity, drugs, and we've been put down because 'we can't get back into society because of our egos or we don't get the money'," said Mr Scotts, the first Australian to be drafted into the US National Football League (NFL).

Colin Scotts, former NFL player, will be donating his brain to the Australian Sports Brain Bank at Sydney University's Brain and Mind Centre. Credit:Wolter Peeters

"But in reality for a lot of us the aggressive spells, the issues, come down to mental illness, and I believe it's from all the banging on the head."