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 said she "cannot accept" the "unfairly harsh" ban - and will appeal.
Sharapova will challenge the suspension, which is backdated to 26 January 2016, at the Court of Arbitration for Sport (Cas).
In a statement, she said the tribunal concluded her offence was "unintentional" and that she had not tried to use a "performance-enhancing substance".
But she claimed the ITF had asked the tribunal to impose a four-year ban, adding it "spent tremendous amounts of time and resources trying to prove I intentionally violated the anti-doping rules".
The tribunal ruling said Sharapova 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.
It treated both results as a single anti-doping violation.
The London 2012 Olympic silver medallist added: "I have missed playing tennis and I have missed my amazing fans... your love and support has gotten me through these tough days.
"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."
The ITF will not appeal against the tribunal's decision.
However, the World Anti-Doping Agency (Wada) said it would "review the decision, including its reasoning" and decide whether to appeal, foreign media reports.