Transgender swimmer Lia Thomas failed in her challenge to rules that stop her from competing in elite women's races because judges ruled she did not have standing to bring the case.
The Court of Arbitration for Sport panel of three judges dismissed Thomas' request for arbitration with the World Aquatics governing body in a ruling released Wednesday.
The decision prevents the American from having any chance of competing at the Paris Olympics, which begin July 26.
"The CAS decision is deeply disappointing," Thomas said in a statement. "Blanket bans preventing trans women from competing are discriminatory and deprive us of valuable athletic opportunities that are central to our identities. The CAS decision should be seen as a call to action to all trans women athletes to continue to fight for our dignity and human rights."
World Aquatics banned transgender women who have been through male puberty from competing in women's races. It also created an "open" category for which transgender athletes would be eligible.
Thomas had asked the sports court in Switzerland to overturn the rules approved in 2022 that she said were invalid, unlawful and discriminatory.
Thomas swam for the University of Pennsylvania and won an NCAA title in meets that are outside the World Aquatics competitive system, in which she was not registered.
"The panel concludes that she lacks standing to challenge the policy and the operational requirements in the framework of the present proceeding," the court said in its ruling.
The judges said USA Swimming had no authority "to modify such scope of application" of the world governing body's rules.
World Aquatics said it welcomed the CAS decision in a case "we believe is a major step forward in our efforts to protect women's sport."
ESPN's Katie Barnes, The Associated Press and Reuters contributed to this report.