Maria Sharapova has revealed she failed a drugs test at the Australian Open in January.
The 28-year-old former world No 1 tested positive for meldonium, a substance she has been taking since 2006 for health issues.
Maria Sharapova, a five-time Grand Slam champion, is provisionally suspended from March 12 pending further action.
“I did fail the test and take full responsibility for it,” she said.
“For the past 10 years I have been given a medicine called mildronate by my family doctor and a few days ago after I received a letter from the ITF [International Tennis Federation] I found out it also has another name of meldonium, which I did not know.”
Maria Sharapova won the Wimbledon title as a 17-year-old in 2004.
The Russian, who lives in Florida, provided the anti-doping sample in question on January 26, the day she lost to Serena Williams in the Australian Open quarter-finals.
The World Anti-Doping Agency (WADA) analyzed the sample and returned a positive for meldonium, leading to the Russian being charged on March 2.
“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 that medicine for the past 10 years,” said Maria Sharapova.
“But on January 1 the rules had changed and meldonium became a prohibited substance, which I had not known.”
Maria Sharapova added: “I received an email on December 22 from WADA about the changes happening to the banned list and you can see prohibited items – and I didn’t click on that link.”
She has been the highest-earning female athlete in the world for the past 11 years, according to the Forbes list.
She first reached world No 1 in August 2005 and is currently seventh in the rankings – but she has played just four tournaments since Wimbledon last July as she struggled with an arm injury.
Maria Sharapova, who turns 29 in April, hopes to be able to return to tennis in the future.
However, there had been speculation Maria Sharapova was going to announce her retirement and a large media contingent gathered for the Los Angeles news conference, which was streamed live online.
“I know many of you thought that I would be retiring today but if I was ever going to announce my retirement it would not be in a downtown Los Angeles hotel with this fairly ugly carpet,” she said.
Women’s Tennis Association (WTA) president Steve Simon said he is “very saddened” at Maria Sharapova’s failed test.
“Maria is a leader and I have always known her to be a woman of great integrity,” he added.
“As Maria acknowledged, it is every player’s responsibility to know what they put in their body and to know if it is permissible.
“This matter is now in the hands of the Tennis Anti-Doping Program and its standard procedures. The WTA will support the decisions reached through this process.”