Tennis-Sharapova fails drug test, Nike suspends ties

* Russian admits to failing test at Australian Open

* Seventh athlete in a month to test positive for meldonium

* Sponsor Nike suspends ties with Sharapova (Recasts lead with Nike suspending ties, adds details from statement)

By Mark Lamport-Stokes

LOS ANGELES, March 7 (Reuters) - Russian tennis star Maria Sharapova said on Monday she had failed a drug test at the Australian Open due to a substance she was taking for health issues, leading longtime sponsor Nike to announce it was suspending ties during the investigation.

The 28-year-old Sharapova, a five-time grand slam champion and the highest paid woman in sports, 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 (WADA) 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 number one Sharapova told a news conference in a downtown Los Angeles hotel.

Nike, the world's largest sportswear maker, said it was "saddened and surprised" by the news and released a statement saying it was putting ties on hold with the player.

"We have decided to suspend our relationship with Maria while the investigation continues," it said.

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.

TAKEN MELDONIUM FOR 10 YEARS

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."

WADA declined to comment until ITF issues a final decision.