Russia's sole track and field competitor at the Rio Olympics, Darya Klishina, has been suspended from the Games, a source told Reuters.
No details of the suspension were immediately available, but the Court of Arbitration for Sport said it had received an appeal from the long-jumper, against an eligibility issue of the international athletics federation (IAAF).
The source, close to the proceedings, who spoke on condition of anonymity said the long jumper had been suspended as new evidence had emerged in relation to a World Anti-Doping Agency report - the McLaren report - and Klishina.
CAS was expected to rule on her appeal either on Sunday or Monday. The IAAF were expected to issue a statement later in the day.
Russian officials in Rio and Moscow were not immediately available to comment.