Russian tennis star Maria Sharapova, the highest-paid woman in sports, said on Monday that she 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 Sharapova, a five-time grand slam champion, will be provisionally suspended starting 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 as of Jan. 1. "I made a huge mistake. I let my fans down and I let the sport down," said Sharapova, a teenage tennis prodigy who became the third-youngest Wimbledon champion. "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," former world No.1 Sharapova told a news conference in a downtown Los Angeles hotel.

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 $29.5 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."

The World Anti-Doping Agency, or WADA, declined to comment until ITF issues 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.