Bugaychuk, who turned 27 today, tested positive for the drug at the 2016 Men's European Water Polo Championship in Belgrade, Russian news agency TASS reported.

He is the 23rd Russian known to test positive for the drug, 21 of whom have been identified publicly. 

Russia's Sports Minister Vitaly Mutko had warned last week that the number of Russians testing positive for meldonium could reach as high as 30.  

"Meldonium’s fallout in low concentration was discovered in Bugaychuk’s doping test," a source told TASS.

"He never kept it a secret taking meldonium since it used to be legal. Last time he took it in October, when the medicine was still legal.

"The level of concentration revealed by the test shows that he took the substance last time in October.

"He [Bugaychuk] refused from Sample B test and wrote a relevant letter to the FINA [the International Swimming Federation].

"FINA suspended him immediately from all tournaments until a decision on behalf of an expert commission."

According to TASS, the test which produced the positive sample was taken on January 18 after Russia had been beaten 15-5 in the quarter-final by hosts Serbia.

"After that,Bugaychuk was tested twice for performance enhancing drugs and each time results were negative," the source told TASS.

"Almost all of the team’s players were tested for doping at that time and all results were negative."

Bugaychuk was also a member of Russia's squad that finished bottom of their group at last year's World Aquatics Championships in Kazan. 

Numerous other Russians have failed for meldonium, a drug developed to help treat patients suffering from heart conditions, in recent weeks after the heart-attack drug was added to the banned list of the World Anti-Doping Agency (WADA) on January 1.

The drug hit the headlines when five-time Grand Slam champion Maria Sharapova of Russia announced she had tested positive for the substance at the Australian Open in January at a press conference on March 7.

One of the most high-profile Russian athletes to have failed a test because of meldonium use is swimmer Yuliya Efimova, a four-time world champion.

She won the 100 metres breaststroke title at last year's home World Championships in Kazan and is considered Russia's leading swimmer.

Track cyclists Anastasia Chulkova, winner of the points race at the 2012 World Track Cycling Championships in Melbourne, and Pavel Yakushevsky, a team sprint bronze medallist at the 2013 European Track Cycling Championships, were revealed to have tested positive for meldonium last week.

Evgeny Saleev, a 2014 World Championship silver medallist in wrestling, were among five from the global superpower to be implicated this week, along with fellow wrestler Sergey Semenov and athletics trio Gulshat Fazletdinova, Andrey Minzhulin and Olga Vovk.

Others include speed skaters Pavel Kulizhnikov, Semyon Elistratov and Ekaterina Konstantinova, as well as ice dancer Ekaterina Bobrova.

Husband and wife rugby players Alexei Mikhaltsov and Alena Mikhaltsova have been provisionally suspended, while biathlete Eduard Latypov and volleyball player Alexander Markin are further Russian cases.

International Sambo Federation President Vasily Shestakov has also revealed that four sambists, including two from Russia, have tested positive for meldonium.

Developed in Latvia, meldonium was moved from the monitored to the prohibited list by WADA due to “evidence of its use by athletes with the intention of enhancing performance”.

It has been claimed that the drug was used by Soviet troops fighting in Afghanistan. 

Ben Nichols, a WADA spokesman, had claimed that the number of worldwide meldonium cases stood at 123 as of last Thursday (March 24). 

Besides the 23 Russians known to have failed for meldonium, seven athletes from other countries, including three from Ukraine, have returned positive tests for the drug. 

List of Russians known to have tested positive for meldonium