The former world number one from Russia yesterday 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 would halt its relationship with her as the case moves forward.
"We are saddened and surprised by the news about Maria Sharapova," Nike said in a statement.
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.
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"I did fail the test and I take full responsibility for it," a sombre Sharapova said at a press conference at a downtown Los Angeles hotel yesterday.
"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."
"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.
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- 'Very saddened': WTA boss -
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 USD 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.
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.