Los Angeles - Five-time Grand Slam tennis champion Maria Sharapova said on Monday she failed a dope test at the Australian Open, and isn't sure what punishment she'll face for her "huge mistake."
Health24: Why did Maria Sharapova take Meldonium?
The former world number one from Russia said a change in the World Anti-Doping Agency's banned list for 2016 led to an inadvertent violation, for which she will be "provisionally suspended" by the International Tennis Federation.
In a sign of what the affair could mean to Sharapova's mass of money-spinning endorsements, US sportswear maker Nike said it was "saddened and surprised" by the news.
"We have decided to suspend our relationship with Maria while the investigation continues."
Sharapova tested positive for Meldonium, a drug she said she had been taking since 2006 but was only added to the banned list this year.
"I did fail the test and I take full responsibility for it," Sharapova said at a press conference at a downtown Los Angeles hotel.
"I made a huge mistake. I let my fans down. I let my sport down that I've been playing since the age of four that I love so deeply," added Sharapova, her voice wavering.
"I know that with this, I face consequences and I don't want to end my career this way -- and I really hope I will be given another chance to play this game."
The ITF confirmed in a statement that Sharapova had tested positive on January 26 and had accepted the finding when she was notified on March 2.
"Ms Sharapova will be provisionally suspended with effect from 12 March, pending determination of the case," the ITF said.
Sharapova said she was cooperating with the ITF and did not yet know the extent of the sanctions she would face.
Her attorney, John Haggerty, said the positive test could carry a ban of up to four years, but that mitigating circumstances could see a lesser penalty.
Shamil Tarpishchev, head of the Russian tennis federation, told the TASS news agency he believed Sharapova would still have a chance to play at the Rio Olympics in August.
Sharapova, 28, burst onto the international scene as she giggled and grunted her way to the Wimbledon crown in 2004.
She won the US Open in 2006, the Australian Open in 2008 and the French Open in 2012 and 2014.
Her ferocity on the court, business acumen and glamorous looks have all combined to make her a marketing juggernaut and the overseer of such successful ventures as her Sugarpova line of candy.
She has 35 WTA singles titles, more than $36 million in career earnings and is currently ranked seventh in the world.
"I am very saddened to hear this news about Maria," WTA chief executive Steve Simon said in a statement.
"Maria is a leader and I have always known her to be a woman of great integrity. 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."
Australian tennis officials also said they were surprised to learn that Sharapova tested positive in Melbourne.
"Throughout her career Maria has always impressed with her professionalism as a leader and role-model in our sport," Tennis Australia said in a statement, noting she had said she was prepared to "face the consequences" of the result.
Sharapova said she originally began taking Meldonium for a variety of symptoms, including a tendency to become ill often, an irregular EKG heart test and a family history of diabetes.
Meldonium is used to treat heart trouble, including angina and heart failure.
In adding it to the banned list, the World Anti-Doping Agency said there was evidence it has been used by athletes with the intention of enhancing performance.
A string of sports figures have tested positive for it this year, including Russian ice dancer Ekaterina Bobrova, Ukrainian biathletes Artem Tyshchenko and Olga Abramova and Ethiopian-born Swede Abebe Aregawi, the 2013 women's 1500m world champion.
Sharapova has struggled with injuries during her career and has played just three tournaments since Wimbledon last year.
She pulled out of the 2015 US Open with a leg injury and withdrew from the tournament starting this week in Indian Wells, California with a left forearm injury.
Her most recent match was her Australian Open quarter-final loss to long-time rival Serena Williams.
Monday's short-notice press conference promising a "major announcement" had sparked speculation that Sharapova might be preparing to announce her retirement.
"If I was ever going to announce my retirement it would probably not be in a downtown Los Angeles hotel with this fairly ugly carpet," she said in a half-hearted attempt to lighten things up.
Otherwise, she was sombre.
"I have to take full responsibility for it," Sharapova said. "At the end of day, everything you do is about you."