A Russian Olympic athlete who declared her anti-doping stance on a jumper emblazoned with the slogan, "I Don't Do Doping, I Am Za Sport', has tested positive for a banned substance".
The court said that she tested positive for the heart medication trimetazidine and admitted the offense, the fourth doping case to hit the Pyeongchang Olympics and second from Russian Federation.
At the time, she was training in a T-shirt with the words "I Don't Do Doping".
Sergeeva piloted the Russian bobsled team to 12th in the women's competition on Wednesday and denies taking the banned medication, which has not yet been identified.
The IOC will decide on Saturday whether the Russian curling team will be formally reinstated to participate in the closing ceremony.
Meldonium, a widely used anti-ischemia medication, was banned by the World Anti-Doping Agency right at the start of 2016, a move which affected hundreds of athletes who were caught off-guard by the ban.
"I can tell you that on the 13th it was clean, but on the 18th it gave a positive result for the heart medication", he said.
Their result has been annulled and Sergeeva, the second OAR athlete to test positive at Pyeongchang 2018, has been stripped of her accreditation.
"Sergeeva refused to open the "B" sample", Makarova said.
The two Russian doping cases, involving a medal-winning curler and a bobsledder, make it very tough for the IOC to lift the suspension, despite a large body of support within the organization for ending Russia's Olympic punishment.
In a statement, the CAS anti-doping division confirmed Sergeeva, competing for the Olympic Athletes from Russia (OAR), had admitted a doping offence.
"It's a lot of emotion for us and just being there, enjoy what we did, I feel it's that we need to remember from the Games", she said.
It is thought Russia's chances of having their suspension lifted have been drastically reduced by the second doping case. Chinese swimmer Sun Yang, an Olympic gold medalist, was banned for three months in 2014 by his country's sports authorities after testing positive for the substance. Officials have pointed out that a "partial" lifting of the ban is one option for the IOC.
Russian Federation had nearly been banned from participating in this Olympic Games due to massive doping violations at the Sochi-2014 event.
Despite Russia's appeal to the International Olympic Committee, some of its athletes were losing hope of getting their flag back. The bobsledder did not have a prescription for the drug.