Russian tennis star Maria Sharapova, the highest-paid sportswoman in the world, failed a drug test at the Australian Open due to a substance she has been taking for 10 years for health issues.
The 28-year-old, a five-time grand slam champion, will be provisionally suspended from March 12, the International Tennis Federation (ITF) said.
She is the seventh athlete in a month to test positive for meldonium, which is used to treat diabetes and low magnesium, and was only banned by the World Anti-Doping Agency (WADA) as of January 1.
"I made a huge mistake. I let my fans down and I let the sport down," the former world No.1 told a news conference.
"I take full responsibility for it.
"I know that with this I face consequences and I don't want to end my career this way. I really hope that I will be given another chance to play this game."
The ITF's anti-doping program calls for a four-year suspension for a positive test, but that ban can be reduced in various circumstances, such as for first-time offences or if the player shows no significant fault or negligence. If a player bears no fault or negligence, there is no suspension.
According to Forbes, she earned $US29.5 million ($NZD43.47 million) in 2015, mostly from endorsements.
Sharapova said her family doctor had been giving her mildronate, which is also called meldonium, for 10 years after she frequently became sick, had irregular EKG results, a magnesium deficiency and a family history of diabetes.
"It is very important for you to understand that for 10 years this medicine was not on WADA's banned list and I had been legally taking the medicine. But on January the first, the rules have changed and meldonium became a prohibited substance," she said.
WADA declined to comment until the ITF issued a final decision.
Meldonium is used to treat chest pain and heart attacks among other conditions, but some researchers have linked it to increased athletic performance and endurance. It is listed by WADA among its prohibited metabolic modulators, along with insulin, and some researchers say it can also help recovery.
It is not approved in the United States but is available in Russia.
Over the past month, Russian cyclist Eduard Vorganov, Russian figure skater Ekaterina Bobrova, Ethiopia-born athletes Endeshaw Negesse and Abeba Aregawi and Ukraine biathletes Olga Abramova and Artem Tyshchenko have all tested positive for meldonium.
Sharapova is the most prominent tennis player to test positive for a banned substance in recent years.
Croatia's Marin Cilic was banned for nine months in 2013 after testing positive for a prohibited stimulant, though the suspension was cut to four months on appeal.
Former world No.1 Martina Hingis retired after receiving a two-year suspension for a positive cocaine test in 2007, though the Swiss denied taking the drug.
Last year, the sport banned American player Wayne Odesnik for 15 years after his second doping violation, testing positive for steroids and other banned substances.
Sharapova is the biggest name in sport to test positive since New York Yankees baseball slugger Alex Rodriguez was banned for a year in 2013 after using performance-enhancing drugs and American cyclist Lance Armstrong was banned for life from racing in 2012 after a US Anti-Doping investigation.
Sharapova, one of the most popular figures in global sports, has long been a favourite with her sponsors.
Cosmetics maker Avon Products Inc declined to comment on its endorsements. Nike Inc, the world's largest footwear maker and another sponsor, did not immediately respond to a request for comment.
Steve Simon, CEO of the Women's Tennis Association, said in a statement he was saddened to hear the news.
"Maria is a leader and I have always known her to be a woman of great integrity," he said.
"Nevertheless, as Maria acknowledged, it is every player's responsibility to know what they put in their body and to know if it is permissible. The WTA will support the decisions reached through this process."
Sharapova, who has struggled with a series of injuries in recent years, has not competed since she lost to Serena Williams in the quarter-finals of the Australian Open in January.Reuters