A Russian athlete who won bronze in the mixed curling at the Winter Olympics has failed a preliminary drug test, putting his medal into jeopardy and throwing the spotlight on the decision to welcome 168 Russian athletes to Pyeongchang after the country was nominally banned for state-sponsored doping in Sochi four years ago.

The athlete has not been officially named but sources have confirmed reports in Russia that it is Alexander Krushelnytsky, who was found to have meldonium in his urine after playing in the mixed-curling tournament as a member of the Olympic Athletes from Russia team alongside his wife, Anastasia Bryzgalova.

The substance, which is used to treat heart attack victims, has been prohibited since 2016. It was commonly used by Russian athletes before that, including Maria Sharapova, who was banned for 15 months after she failed a test at the Australian Open in January 2016.

In a statement the International Olympic Committee said: “On the one hand it is extremely disappointing when prohibited substances might have been used, but on the other hand it shows the effectiveness of the anti‑doping system at the Games which protects the rights of all the clean athletes.”

According to the Russian newspaper Sport Express, Krushelnytsky’s B sample will be opened on Monday. If it is found to contain meldonium, he and his wife are likely to lose their medal.

The website Inside the Games has reported, however, that Krushelnytsky has told Russian officials he fears a team-mate who was not selected for the Winter Olympics spiked his drink with meldonium at a training camp before he travelled to South Korea.

A press attache for the OAR team did not name the athlete but confirmed: “Today, the headquarters of our delegation received an official notification from the IOC about a possible violation of the anti-doping rules.

“We do not call the name of the athlete or athletes, as well as the sport prior to the results of the opening of the sample B.”

The timing could not have been worst for Russia, who were hoping that their athletes would be able to march under their own flag at the closing ceremony next Sunday.

Disappointment for the Great Britain’s women’s curling team after a controversial decision leads to Sweden defeat. Photograph: Dean Mouhtaropoulos/Getty Images

Muirhead bemoans controversial Sweden defeat

Great Britain’s women curlers controversially lost against Sweden after the skip Eve Muirhead was penalised for releasing the final stone too late.

Replays of her hog line violation were inconclusive but the decision stood following testing of the technology – a red flashing light on the stone – which alerts referees to any foul play. The violation meant Team GB’s final stone was removed from play leaving Sweden to clinch victory – and Muirhead bemused.

She said: “It is the first stone I think I have hogged in my life and I guess when it comes at a time like that it is horrible. But it just makes it worse when you see it and it doesn’t look like it is. We did get the stone tested and the stone is fine so there is nothing we can do. We have to move on.”

Britain’s women curlers now have a 3-3 win-loss record and may need to win their next three games to make the semi-finals.