Caster Semenya will not be taking part in the athletic World Championships latest this year after a Swiss court overturned its ruling on testosterone regulations.
The double Olympic champion has been in the middle of a legal battle with the International Association of Athletics Federations (IAAF), which has introduced a rule that would require she take medication to limit her testosterone levels.
In June, the Federal Supreme Court of Switzerland initially ordered the IAAF temporarily suspend its regulation until the appeal launched by Semenya, who has a difference of sexual development (DSD), had been finalised.
This temporary suspension would have allowed the South African athlete to compete in the World Championships in Doha this September, where she had hoped to defend her 800m title.
But the court on Tuesday overturned its decision on the suspension, barring Semenya from taking part. A full report is expected to be released later on Wednesday.
Semenya, who has XY chromosomes, said she was "very disappointed" at the decision at being "kept from defending my hard-earned title."
She added: "This will not deter me from continuing my fight for the human rights of all of the female athletes concerned."
The IAAF regulations stipulate that athletes with differences in sexual development can only take part in races from 400m to a mile if they take medication to limit their levels of the primary male hormone.
Semenya has previously accused the IAAF of using her as "a human guinea pig" by requiring her to take such medication that she says makes her feel "constantly sick".