maria sharapova

In an essay, Sharapova says she is stepping away from the sport she's been playing for 28 years. She's a five-time Grand Slam champion and former No. 1, who also served a 15-month ban for doping.

The tennis star was suspended from international competition after testing positive for the banned drug meldonium. She will be eligible to play again beginning in April 2017.

The World Anti-Doping Agency considers whether a drug can unfairly improve athletes' chances of winning — and also whether it could harm them — when deciding to blackball a drug.

An independent tribunal has ruled that Sharapova is ineligible after testing positive for meldonium. She said she didn't know at the time that the substance had been banned starting early this year.

Brands such as Nike and Porsche have distanced themselves from tennis star Maria Sharapova, who has long been the world's highest-paid female athlete.

The five-time Grand Slam champion said she was notified by the International Tennis Federation several days ago that she tested positive for meldonium.