Caster Semenya has lost case against athletics’ governing body, IAAF, meaning it will be allowed to restrict testosterone levels in female runners.
The Court of Arbitration for Sport issued its ruling on Wednesday.
The IAAF wants female athletes with differences in sexual development to take testosterone blockers.
That ruling means officials can implement new rules on testosterone levels.
But Caster said it had “serious concerns as to the future practical application” of the new rules.
Caster Semenya, 28, had said the regulations were “unfair” and that she wanted to “run naturally, the way I was born”.
Now the Olympic, world and Commonwealth champion at 800m – and other athletes with differences of sexual development (DSD) – must either take medication in order to compete in track events from 400m to the mile, or change to another distance.
Cas found that the rules for athletes with DSD were discriminatory – but that the discrimination was “necessary, reasonable and proportionate” to protect “the integrity of female athletics”.
However, Cas set out serious concerns about the application of the rules, including:
Worries that athletes might unintentionally break the strict testosterone levels set by the IAAF;
Questions about the advantage higher testosterone gives athletes over 1500m and the mile;
The practicalities for athletes of complying with the new rules.
Cas has asked the IAAF to consider delaying the application of the rules to the 1500m and one mile events until more evidence is available, BBC Sports reports.
Semenya would still be eligible to compete at the Diamond League meet in Doha on Friday.