It is just one case, brought by just one athlete, against a single organisation. But Caster Semenya’s challenge to the IAAF’s testosterone rules for female athletes, which begins on Monday at the court of arbitration for sport, may yet be as far-reaching and profound as the Bosman ruling.

It is not only that the court holds the career of the brilliant Olympic 800m champion in its hands. That, alone, is a weighty enough responsibility. But it also knows that its ruling, which will be announced next month, will be pored over by other organisations trying to wade through the murky waters where gender, biology and identity converge.

That includes the International Olympic Committee. As Joanna Harper, who advises it on model regulations for transgender athletes, tells me “the IOC is waiting to see what happens in the Semenya case” before announcing its testosterone limits for transgender athletes in women’s events for the 2020 Summer Olympics in Tokyo.

As things stand the IOC plans to reduce the level from 10 nanomoles per litre to five, because 99% of women have testosterone levels less than three nanomoles per litre. The reason, as Harper, a medical physicist who was born male but later transitioned, explains, is because “if you’re competing in the women’s division, you should do so with women’s hormone levels. I understand just how much difference they make.”

The International Association of Athletics Federations’ proposed policy for female athletes with differences in sex development (DSDs), such as Semenya, is very similar. It too wants them to reduce their testosterone levels to five nanomoles per litre in order to compete internationally at distances from 400m to a mile to create “a level playing field” for other female athletes.

Inevitably such a policy would have a disastrous effect on Semenya’s performances – with the sports scientist Ross Tucker estimating it would make her between five to seven seconds slower over 800m. Asking someone to take medication to suppress their natural testosterone levels also makes many queasy, to say the least. The UN human rights special procedures body has even suggested that the IAAF’s planned regulations “contravene international human rights”.

Those looking for science to provide an easy resolution to the case are likely to be disappointed too. Semenya’s legal team argue that her advantages are no different from other genetic variations celebrated in sport – and that “her genetic gift should be celebrated not discriminated against”. But the IAAF maintains these gifts provide a massive advantage. It says that while most females have testosterone levels ranging from 0.12 to 1.79 nmol/L, female DSD athletes – who are often born with testes and get similar increases in muscle size, strength and haemoglobin levels as a male does after puberty – are usually in the normal adult male range, which is from 7.7 to 29.4 nmol/L.

As Dr Stéphane Bermon, who heads the IAAF’s health and science department, explains: “Historically the reason why we have separate male and female categories is that otherwise females would never win any medals. Testosterone is the most important factor in explaining the difference. We are talking about females competing with levels similar to males. Very often it is more than 20 or 25nmol/L. So it is very high.”

But it is not as clearcut as that. A paper published by Bermon in the British Journal of Sports Medicine in 2017, which claimed that elite women runners with high testosterone levels performed as much as 3% better than those with lower levels, has been heavily criticised by three academics – Roger Pielke, Erik Boye and Ross Tucker – who say that 17-32% of the data was erroneous. That looks immensely damaging to the IAAF’s case.

But whatever Cas decides it is hard to see how it can balance the rights of Semenya and DSD athletes with the broader need to protect women’s sport – or resolve the inherent tensions between fairness and inclusivity. Regardless of what happens, the question remains: if we accept that there should be separate categories for men and women in elite sport, can it be done in a manner that satisfies everybody?

It was notable that the IAAF’s lawyer Jonathan Taylor grouped DSD and transgender athletes together last week when talking of the potential consequences of the verdict. “If Cas rules that legal recognition as female is sufficient to qualify for the female category of competition,” he began, “and the IAAF is not permitted to require athletes of female legal sex who have testes and consequently male levels of testosterone to reduce those levels, then DSD and transgender athletes will dominate the podiums and prize money in sport, and women with normal female testosterone levels will not have any chance to win.”

That is a big claim – and, if correct, would have enormous consequences for sport. Meanwhile others are asking whether a third category in sport might be a solution. Bermon, who works for the IAAF but speaks in a personal capacity, says he has the “feeling some day it will happen, and probably in five or 10 years”. Another scientist, who is strongly sympathetic to Semenya’s case, suggests that one day there could be a high-testosterone category and a low-testosterone category with no other distinction, or a tall and short category, or weight classes. “I can see that happening,” he says. “After all, the Paralympics have dozens of classifications.”

I am not sure it is that easy, but it is certainly food for thought – and not just for the lawyers at Cas.