According to a bombshell report in News Corp newspapers on Thursday, the club made the player sign the agreement in a bid to exonerate itself and its medical staff from future court action.
The deal with the unnamed footballer, who is still an active AFL player, was signed two years ago.
The report said the club viewed such an agreement as the only way the player could continue his career given his history of concussions.
The disclosure agreement 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.
The reported deal has been slammed by concussion campaigners, experts and the AFL Players Association (AFLPA) - who were reportedly unaware of the agreement.
"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 provided to News Corp.
"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 added: "The process is contracting out the basic legislative safety net for players in breach of their basic human right to a safe workplace."
Concussion and head trauma is one of the most pressing issues facing the AFL today.
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.
Lifeline 13 11 14
beyondblue 1300 22 4636
