Former world number one Maria Sharapova has revealed she failed a drugs test at the Australian Open.
The Russian, 28, tested positive for meldonium, a substance she has been taking since 2006 for health issues.
The International Tennis Federation (ITF) said the five-time Grand Slam champion would be provisionally suspended from 12 March.
Sportswear company Nike said it was halting its relationship with her until the investigation was complete.
"I did fail the test and take full responsibility for it," said Sharapova, who won Wimbledon as a 17-year-old in 2004.
Sharapova has been the highest-earning female athlete in the world in each of the past 11 years, according to the Forbes list.
With career earnings from tennis alone amounting to almost £26m, she claimed she had taken meldonium "for the past 10 years" after being given it by "my family doctor" but had known the drug as mildronate.
"A few days ago, after I received a letter from the ITF, I found out it also has another name of meldonium, which I did not know," she said.
Sharapova's lawyer, John Haggerty, told Sports Illustrated he was hopeful the player would avoid a lengthy ban.
"We think there is a laundry list of extremely mitigating circumstances that, once taken into consideration, would result in dramatically reducing any sanction that they might want to impose on Maria," he said.