Sergeeva tested positive for the banned heart condition produce trimetazidine two days before her race in Pyeongchang but CAS said in a statement on Monday that the anti-doping violation "likely resulted from a contaminated product."
Sergeeva finished 12th with Anastasia Kocherzhova in the women’s bobsleigh but her team were disqualified as a result of the positive doping test.
CAS said Sergeeva accepted the result of the doping test at the time, however she had since sought to have the suspension lifted. A final decision in the case would be issued "as soon as possible", it added.
Russians competed as neutrals at the Games after the International Olympic Committee (IOC) suspended the country's Olympic committee in December, saying it had found evidence of an "unprecedented systematic manipulation" of the anti-doping system.
The two positive tests in Pyeongchang ended Russia's hopes of being allowed to fly its flag at the Games' closing ceremony.
Russia, which has repeatedly denied state involvement in doping, was subsequently readmitted by the IOC after all other doping tests on its athletes were negative.
(Reporting by Tassilo Hummel and Brian Homewood; Editing by Maria Sheahan and Ken Ferris)
