Officials pointed to revelations that drug violations had been routinely covered up by Russian antidoping authorities, who investigators said broke into supposedly tamper-proof bottles — leaving microscopic scratch marks — and swapped out the steroid-laced urine of Russian athletes, sometimes substituting in the clean urine of different people.

Klishina — who has trained outside Russia, in Florida, for the last three years — was the only Russian athlete cleared to compete by the track organization and the International Olympic Committee. Nearly 70 other applications were rejected.

But in recent weeks, a continuing investigation into Russian doping commissioned by the World Anti-Doping Agency raised questions about Klishina’s drug-test history, suggesting that a urine sample of hers had been tampered with. That sample was taken during the last two years, the court said.

Richard McLaren, a Canadian lawyer who issued a damning report on Russian doping last month and is leading the continuing inquiry, on Sunday confirmed that he had provided the I.A.A.F. with information in the form of affidavits on Klishina that had informed the organization’s decision and were also provided to the sports court.

Asked what the presence of two DNA profiles in one sample signified, Richard Budgett, the medical and scientific director of the International Olympic Committee, said on Monday, “You do not expect to find two people’s urine in the same sample bottle.”

He added, “That would be a case of manipulation.”

Greene, Klishina’s lawyer, said her case had partly asserted that the I.A.A.F. did not have the authority to revisit its final decision. It also pointed to her years in the United States, where she was subject to drug tests.

"At this moment,” Klishina wrote on Facebook on Saturday, after she had arrived in Rio, “I cannot help but feel betrayed by a system that is not focused on keeping the sport clean and supporting rank-and-file athletes, but rather seeking victories outside sport arenas.”