Russian curler Alexander Krushelnitsky could be stripped of his Winter Olympics bronze medal after his second sample tested positive for banned substance meldonium.
In a statement, the Russian delegation in Pyeongchang said: “We express our sincere regret over the fact of the incident.”
However, it also says the results suggest he only took meldonium once and that the substance would be “absolutely useless and ineffective” at improving performance.
No data on the test has been provided.
Krushelnitsky, 25, tested positive for meldonium after he and his wife, Anastasia Bryzgalova, came third in the mixed doubles curling.
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Russian curling officials have previously suggested that Krushelnitsky could have been set up by a rival Russian athlete or Russia’s political enemies.
Krushelnitsky, who faces being stripped of his medal, has denied using banned substances, calling the positive tests a “huge shock”.
In a statement, he said: “First of all, I want to apologise to my Olympic teammates and our delegation and all the supporters.
“I can openly confirm that never, at any time that I have been involved in sport, have I ever used any prohibited substances or any other dishonest means of competition.
“I am categorically opposed to doping and have always strived to follow the conformities of all anti-doping rules with maximum attention. In light of that, my positive test for meldonium was a huge shock for me and for Nastya.
“It is a huge blow to my reputation and to my career. Not to mention the fact that only someone with a complete absence of common sense could use doping in any form, especially meldonium, in the lead-up to the Olympic Games, where testing is of the highest level,” he added.
Russia’s curling federation is investigating the incident, along with the Court of Arbitration for Sport (CAS) and the Russian Olympic Committee, which could open a criminal inquiry.
Meldonium is designed for people with heart problems and some believe it can help athletes increase stamina. It was banned by the World Anti-Doping Agency (WADA) in 2016.
Since then, more than 15 Russian athletes have tested positive for it, but all were cleared of doping charges after they proved they had taken the drug before it was prohibited.
Any confirmed cases of doping by Russian athletes at these games could derail Russia’s chances of being officially reinstated in the Olympic fold following its ban for state-sponsored doping at the at the 2014 Winter Olympics in Sochi.