Athletics world body, the IAAF, has banned long jumper Darya Klishina, Russia's only athlete allowed to take part in the Rio Olympics, the Court of Arbitration has confirmed.
Klishina made an immediate appeal to the court against the order, the tribunal said.
The International Association of Athletics Federations banned Russia because of an investigation which said there had been "state-sponsored" doping in Russia.
Klishina was originally allowed to compete in Rio because she was based in the United States and had regular testing outside Russia.
Meanwhile, Bulgarian runner Silvia Danekova branded the World Anti-Doping Agency (WADA) a "mafia in white aprons" who she is unable to fight to clear her name after failing a drugs test soon after arriving in Brazil.
The 33-year-old, who was due to compete in the women's 3000m steeplechase, was thrown out of the Games after testing positive for the banned blood-booster erythropoietin (EPO) during an out-of-competition test on August 1.
Danekova, who denied using drugs to gain advantage, believes she was punished unfairly and highlighted what she said was a "paradox" in the testing of her samples on July 30 and August 1, giving details of PH acidity levels of her urine.
However, the Bulgarian is not planning to take steps to clear her name.
"Let's not be fooled," Danekova was quoted on Saturday in Bulgarian media as telling Bulgarian reporters at the Rio Games. "I cannot fight against them because they are a mafia in white aprons."
The Bulgarian Olympic Committee said in a statement she was suspended after failing the out-of-competition test and her second, B sample, had also tested positive. WADA says it is impartial, objective, balanced and transparent in its pursuit of a doping-free sporting environment.
Danekova, who faces a four-year ban, said she had been tested four times after entering the Olympic Village in Rio and results of the three of the samples were negative.
"At first, I thought it was a joke, I even laughed," Danekova was quoted as saying.
"Then I wanted to jump from the 16th floor ... Then I hoped it's a huge mistake and I thought that they would apologise after that. A long crying started after that while I almost went crazy."