Switzerland’s highest court ruled Monday that two-time Olympic gold medalist Caster Semenya must immediately follow rules passed by track’s governing body that would require her to undergo hormone therapy to compete in certain women’s track events, reversing previous rulings that allowed her to compete pending her appeal.

The latest decision will prevent the 28-year-old South African from defending her world title in the 800 meters at September’s world championships in Qatar, according to her legal team.

In May, the Court of Arbitration for Sport sided with the International Association of Athletics Federations, upholding the organization’s rule that put a cap on permissible testosterone levels for select track and field events. The rule requires any female athletes whose natural testosterone levels exceed a certain threshold to lower their levels, holding that naturally elevated testosterone levels constitute an impermissible competitive advantage.

Switzerland’s Federal Supreme Court last month suspended that rule, allowing Semenya to continue competing without using medication to lower her testosterone levels. But a single judge on the Swiss Federal Supreme Court this week reversed prior rulings, according to Semenya’s legal team, with the court ruling that “the strict requirements and high thresholds for the interim suspension of CAS awards . . . were not fulfilled,” according to Semenya’s representatives.

“I am very disappointed to be kept from defending my hard-earned title, but this will not deter me from continuing my fight for the human rights of all of the female athletes concerned,” Semenya said in a news release.

Her lawyer, Dorothee Schramm, said in the release that Monday’s ruling was “procedural” and “has no impact on the appeal itself. We will continue to pursue Caster’s appeal and fight for her fundamental human rights. A race is always decided at the finish line.”

Semenya has framed her argument about mandated hormonal drug intervention as a violation of “fundamental human rights.” She is believed to have an intersex condition that causes her body to produce higher levels of testosterone. The IAAF, which drafted the regulation upheld by CAS, has maintained this gives her an unfair advantage over other female competitors.

“Such discrimination is a necessary, reasonable and proportionate means of achieving the IAAF’s aim of preserving the integrity of female athletics,” the CAS declared in its decision.

IAAF representatives did not immediately respond to a request for comment Tuesday.

Semenya has said she will not take medication to regulate her body’s hormones and has considered running distances longer than a mile, which are not covered by the IAAF rule.

“I am a woman and I am a world-class athlete. The IAAF will not drug me or stop me from being who I am,” Semenya said in May when she appealed the CAS ruling.

She has dominated in shorter races, claiming gold medals in the 800 meters at the 2012 and 2016 Olympics, world championships in 2009, 2011 and 2017, and golds at the 2018 African championships, Commonwealth Games and Continental Cup. Last month, after the Swiss court suspended implementation of the IAAF rules, she ran the 800 meters at the Prefontaine Classic in California, winning easily.

“First chapter of my life done, looking forward to my second chapter,” Semenya tweeted on Tuesday.