In a press conference, Maria Sharapova, the five-time major champion, announced she failed a drug test at the 2016 Australian Open.
Sharapova, 28, who lost to Serena Williams in the quarterfinals, was widely expected to be announcing her retirement. But instead, she delivered the shocking news that she had been taking a drug, called meldonium, since 2006. The drug was recently placed on the International Tennis Federation's list of banned substances in 2016, said the Russian.
"I failed the test and take full responsibility for that," said Sharapova, who said she's been using the substance for health reasons.
"I had been taking this medicine for the past 10 years," she added, "but on 1 January this became a prohibited substance which I did not know."
Meldonium is listed in a document on the ITF's website as a "metabolic modulator."
"I received an email on 22 December from Wada [World Anti-Doping Agency] about the changes happening to the banned list and you can see prohibited items," Sharapova added during the press conference, "and I didn't click on that link."
Sharapova, who is currently ranked No.7 in the world, has been as high as No.1. Off-court, Sharapova has focused on businesses by collecting millions in endorsement deals with brands such as Nike. In 2012, Sharapova started her own candy business called Sugarpova.
"As meldonium is a non-specified substance under the WADA (and, therefore, TADP) list of Prohibited Substances and Prohibited Methods, Ms Sharapova will be provisionally suspended with effect from 12 March , pending determination of the case," according to ITF in a written statement.
It is unclear how the announcement will effect her endorsement deals. Fortune has reached out to Nike.
Last year, Fortune examined Sharapova's marketability over rival Williams tied to the U.S. Open major tennis tournament.
"I have let my fans down, and let the sport down that I have been playing since age of four that I love so deeply," she said. "I know that with this I face consequences and I don't want to end my career this way. I really hope to be given another chance to play this game."