The secret agreement has been slammed by the AFL Players Association (AFLPA) - who were unaware of it - along with concussion campaigners and experts.
A bombshell report in News Corp newspapers on Thursday morning said a Victorian AFL club had the unnamed player sign the agreement in a bid to exonerate itself and its medical staff from future court action.
The report said the club, confirmed by AAP to be Geelong on Thursday afternoon, viewed such an agreement as the only way the player could continue his career given his history of multiple concussions.
The deal with the unnamed footballer, who is still an active AFL player, was signed two years ago.
The disclosure agreement reportedly required the individual to "take upon yourself the physical and legal risk of loss, damage or injury" arising from future concussions.
It also acknowledged the player was at higher risk of more concussions and could face more serious damage if they suffered further head knocks.
AAP has contacted the AFL and Geelong for comment.
New AFL Commission chair Craig Drummond was the president of the Geelong board at the time the deal was struck.
"Clubs cannot unilaterally contract out of their obligations under the CBA and Standard Playing Contract, nor attempt to avoid their responsibilities under health and safety laws," AFLPA boss James Gallagher said in a statement.
"Importantly, no player is permitted to return to play or train unless they have been deemed medically fit to do so.
"We are in discussions with AFL to better understand the circumstances of this case and ensure this issue is not replicated further at the elite level."
Concussions campaigner Peter Jess told News Corp: "The process is contracting out the basic legislative safety net for players in breach of their basic human right to a safe workplace."
Melbourne coach and former Cats assistant Steven King - who spoke before Geelong were identified as the club in question - was asked about the report on Thursday morning.
"All I'll say about that is that, as a club and me personally, I'd never do anything or ask my players to put themselves at risk. Their health and safety is paramount," King said,
"... as a coach, my opinion is I'd never ask a player to put himself at risk to play, and those decisions are with our doctors and medical team, and that's where, as a coach, I leave them."
Former West Coast premiership coach Adam Simpson was in disbelief.
"From a coach's eye, it's hard to really fathom how you would get to the conclusion that this is a good thing to do. And how it goes up the chain?" Simpson told SEN.
"From a father point of view and a coach point of view, I can't see how you would accept that is the right thing to do for your son or your player."
Concussion and head trauma is one of the most pressing issues facing the AFL.
Multiple players, including former Melbourne star Angus Brayshaw, champion West Coast defender Jeremy McGovern and premiership Magpie Nathan Murphy, were forced into retirement due to repeated concussions.
Several deceased players, including Danny Frawley and Shane Tuck, were posthumously diagnosed with degenerative brain disease Chronic Traumatic Encephalopathy (CTE).
There is also a multimillion dollar concussion class action case against the AFL, led by former Geelong defender Max Rooke, in the Supreme Court of Victoria that is set to go to trial next year.
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