Caster Semenya could be forced to take medication to lower her testosterone levels if new rules are brought in by the International Association of Athletics Federations (IAAF) over hyperandrogenism.
The new regulations, understood by ESPN to be announced on Thursday and introduced in November, will make it mandatory for women whose testosterone is above a certain level to compete in events longer than a mile -- ruling out 400, 800 and 1500 track events -- or take treatment to lower levels to fulfill certain criteria.
The debate over hyperandrogenism was in the headlines back in 2009 when Semenya won 800m gold in the World Championships. She was subjected to a gender test while some of her competitors started questioning her times.
The IAAF looked into the effects of raised testosterone levels on performance in 2011 and their findings recommended an "effective therapeutic strategy" for those whose levels were above a certain quota.
Semenya's times were seemingly effected by these new measures but she still took gold at London 2012 after original 800 winner Mariya Savinova-Farnosova was later disqualified by Court of Arbitration for Sport after being found guilty of doping.
But in 2015, CAS suspended the IAAF regulation after Indian sprinter Dutee Chand challenged the governing body, saying the tests were flawed. CAS responded by challenging the IAAF to prove raised testosterone levels had a direct impact on performance, putting a two-year hold on the regulations and allowing the likes of Semenya to compete medication-free. The South African comfortably won 800m gold at the 2016 Rio Games.
A year later a medical study, commissioned by the IAAF, was published which said higher testosterone levels gave female athletes a "significant competitive advantage" across the 400, 400 hurdles, 800, hammer throw and pole vault events. These were presented to CAS but it delayed a definitive decision.
The IAAF Council met in March, with President Sebastian Coe saying at the time: "It is clear that this is one of the toughest subjects the council and I have been discussing.
"I want to make one point crystal clear, this is not about cheating, no athletes have cheated. This is about our responsibility to ensure, in simple terms, a level playing field."
"We were asked by CAS to provide evidence of the magnitude of the advantage, which we now have. Based on this information the Council approved a request to revise our competition regulations for track events over distances of 400 metres and one mile, including one mile."
The decision will likely provoke outcry from some corners of the athletics world, with Yale Professor Katrina Karkazis previously saying the approach was blinkered.
"Semenya's athleticism was attributed to a single molecule -- testosterone -- as though it alone earned her the gold, undermining at once her skill, preparation and achievement," Karkazis wrote in the Guardian in 2016.
Semenya has stayed quiet on the matter of late but did suggest she was looking to longer distances after completing Commonwealth Games gold across the 800 and 1500.
"I'm still 27, when I do my long runs I feel like I can still fit into distance running. So for me, this is more than a game," she said.