Maria Sharapova has been banned for two years by the International Tennis Federation for using a prohibited drug.
The Russian was provisionally banned in March after testing positive for meldonium at January’s Australian Open.
The heart disease drug, which 29-year-old Sharapova says she has been taking since 2006 for health issues, became a banned substance on 1 January 2016.
The five-time Grand Slam winner says she will appeal against the ban, which is backdated to 26 January 2016.
“I cannot accept an unfairly harsh two-year suspension,” she wrote on Facebook.
“With their decision of a two-year suspension, the ITF tribunal unanimously concluded that what I did was not intentional.
“The ITF asked the tribunal to suspend me for four years – the required suspension for an intentional violation – and the tribunal rejected the ITF’s position.
“I intend to stand for what I believe is right and that’s why I will fight to be back on the tennis court as soon as possible. I will immediately appeal to the Court of Arbitration for Sport.”
The ITF said Sharapova also tested positive for meldonium in an out-of competition test on 2 February, as well as in the aftermath of her Australian Open quarter-final defeat by Serena Williams on 26 January.
The World Anti-Doping Agency said in April that scientists were unsure how long meldonium stayed in the system, and suggested athletes who tested positive before 1 March could avoid bans, provided they had stopped taking it before 1 January.
However, Sharapova had already admitted she continued taking the substance past that date, saying she was unaware it had been added to the banned list as she knew it by another name – mildronate.
In reaching its verdict the ITF recognised Sharapova had not intentionally broken anti-doping rules, as she did not know that mildronate contained a banned substance from January of this year.
But the federation said the Russian was “the sole author of her own misfortune”, as she had “failed to take any steps to check whether continued use of the medicine was permissible”.