Olympic 800 metres champion Caster Semenya of South Africa goes to the Court of Arbitration for Sport on Monday to challenge proposed rules that would force her to lower her testosterone levels.
The South African government has said the rules proposed by track and field's governing body, the International Association of Athletics Federations (IAAF), specifically target Semenya and has called them a "gross violation" of her human rights.
The controversial rules would force so-called "hyperandrogenic" athletes or those with "differences of sexual development" (DSD) to take drugs to lower testosterone levels below a prescribed amount if they wish to compete.
The rules were to have been introduced last November but have been put on hold pending this week's hearings at the Lausanne-based CAS which Semenya is expected to attend. A judgement is expected by the end of March.
The issue is highly emotive.
When British newspaper The Times reported last week that the IAAF would argue that Semenya should be classified as a biological male -- a claim later denied by the IAAF -- she hit back, saying she was "unquestionably a woman".
In response to the report, the IAAF -- stressing it was referring in general terms, not to Semenya in particular -- denied it intended to classify any DSD athlete as male.
But in a statement, it added: "If a DSD athlete has testes and male levels of testosterone, they get the same increases in bone and muscle size and strength and increases in haemoglobin that a male gets when they go through puberty, which is what gives men such a performance advantage over women.
"Therefore, to preserve fair competition in the female category, it is necessary to require DSD athletes to reduce their testosterone down to female levels before they compete at international level."
Semenya is not alone -- the two athletes who finished behind her in the Rio Olympics 800m, Francine Niyonsaba of Burundi and Kenya's Margaret Wambui, have also faced questions about their testosterone levels.
But it is the 28-year-old South African, who also won the 2012 Olympic gold and has three world titles to her name, who has led opposition to the proposed rules.
"She looks forward to responding to the IAAF at the upcoming CAS hearing," Semenya's legal team said, adding that "her genetic gift should be celebrated, not discriminated against".
Led by Sports Minister Tokozile Xasa, South Africa's government argues that the rules are "discriminatory".
"What's at stake here is far more than the right to participate in a sport. Women's bodies, their wellbeing, their ability to earn a livelihood, their very identity, their privacy and sense of safety and belonging in the world, are being questioned," Xasa said on Friday.
The minister warned that if the rules were implemented, they had the potential to hinder any "little girl growing up in an African village with dreams of becoming a top sportswoman."
Athletics South Africa has pledged its "unqualified support" for Semenya and she has received support from other sports.
Cricket South Africa said it stood behind the "national icon" and denounced the IAAF regulations as "an act of discrimination" against women in sport.
And on Sunday, tennis great Martina Navratilova threw her weight behind Semenya.
The 18-time Grand Slam singles winner said it was significant that the change would only apply to female athletes competing in distances from 400m to a mile.
"Leaving out sprints and longer distances seems to me to be a clear case of discrimination by targeting Semenya," Navratilova wrote in Britain's Sunday Times newspaper.
"And can it be right to order athletes to take medication? What if the long-term effects proved harmful?... I hope she wins."