Jordan Chiles says she has been left “heartbroken” by the decision to strip her of her Olympic bronze medal and says she has been exposed to racially motivated abuse on social media.

The US gymnast was initially given bronze in the floor exercise at the Paris Olympics after an appeal over how the judges scored her routine was accepted and she moved from fifth to third place. However, the Romanian Olympic Committee said the appeal had been filed four seconds after the one-minute time limit. The Court of Arbitration for Sport (Cas) then voided Chiles’s appeal and the IOC ordered the American to return the medal. Romania’s Ana Barbosu was promoted to third while Chiles dropped back to fifth. The Romanians had asked for both gymnasts to be given bronze.

Chiles took herself off social media after the decision but returned on Thursday to explain the effect the situation has had on her.

“I have no words. This decisions feels unjust and comes as a significant blow not just to me but to everyone who has championed my journey,” Chiles wrote. “To add to the heartbreak, the unprompted racially driven attacks on social media are wrong and extremely hurtful.”

USA Gymnastics submitted evidence it said showed Chiles’s appeal had been within the time limit. But Cas dismissed the appeal and said its decision cannot be changed “even when conclusive new evidence is presented”.

Chiles said she would continue to fight for her bronze medal. She also won gold in the team event alongside her US teammates.

“I will approach this challenge as I have others – and I will make every effort to ensure that justice is done,” Chiles wrote. “I believe that at the end of this journey, the people in control will do the right thing.”

USA Gymnastics could take the case to the Swiss Federal Tribunal, which can hear appeals against Cas decisions, although the tribunal rarely overrules such decisions. It has also emerged that the head of the Cas panel on Chiles’s case, Dr Hamid G Gharavi, has performed legal work for the Romanian government. Cas told the New York Times that Gharavi had disclosed his work with the Romanian government and none of the parties in the Chiles hearing had objected.

Former Olympic champion Nadia Comaneci said that the saga had taken its toll on all the gymnasts involved.

“I can’t believe we play with athletes mental health and emotions like this … Let’s protect them,” Comaneci posted on X last week.