The AFL has told transgender footballer Hannah Mouncey she is not eligible to be selected in Wednesday's AFL Women's draft.
The league announced the landmark ruling less than 24 hours before the national selection meeting is set to take place in Melbourne.
Having previously played for the Australian men's handball team, Mouncey began a gender transition in 2015 and played eight games for Ainslie this season in the Canberra women's competition.
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The 190cm, 100kg ruck played eight games for Ainslie in Canberra's women's competition this season and kicked 17 goals.
"Good luck to all the girls who nominated for the AFLW draft tomorrow, especially my mates from Canberra," Mouncey tweeted after the decision was announced.
"I can't wait to see you all at the highest level and to play with and against you back in Canberra next year."
It is understood an AFL sub-committee rejected her draft nomination based on an exception in the Victorian Equal Opportunity and Human Rights Commission's guidelines, 'Trans and gender diverse inclusion in sport - complying with the Equal Opportunity Act 2010'.
The exception is to ensure players don't have an unfair competitive advantage in single-sex competitions where the strength, stamina or physique of players is relevant.
"The sub-committee's decision took into account the stage of maturity of the AFLW competition, its current player cohort and Ms Mouncey's individual circumstances," an AFL statement read.
"This decision solely relates to Ms Mouncey's nomination for the 2018 AFLW draft and participation in the 2018 AFLW competition.
"Ms Mouncey may nominate for future AFLW drafts and for registration in other Australian Football competitions."
The recreational nature of state-based women's leagues - as opposed to the semi-professional AFLW - is understood to be the key factor in her continued participation.
The sub-committee was made up of AFL commissioners Jason Ball, Gabrielle Trainor and Major General Simone Wilkie, AFL general manager inclusion and social policy Tanya Hosch and AFL general counsel Andrew Dillon.
The process included consultation with Mouncey, her management, the AFLPA, the Australian Sports Commission and Pride in Sport.
The AFL follows International Olympic Committee protocols which state an athlete must prove their testosterone count is below a certain level.
It is understood Mouncey meets those requirements.
However, AFL football chief Steve Hocking said before the ruling was made public that it was not just a case of applying Olympic standards to the AFL.
"There have been a lot of references around the IOC and so forth and their criteria," Hocking told AFL Trade Radio.
"But the AFL game is quite different to a number of those sports."
In the past, Mouncey has opened about being a transgender person playing sports in Australia.
"Sports really has to play a role in being accepting and supporting people through a transition," she said in a YouTube video.
"Especially men's sport, [it] is a very masculine environment and it is very intimidating.
"Coming out, I had no idea, I was really worried about how people would take it. But they were fantastic.
"It really can, in many ways, make their transition a success or a failure socially."
