Marin Cilic has fought many battles on the court but the Croatian star may face his biggest fight in the court when he appeals against his nine month doping ban.
Currently ranked 24th in the world, Cilic tested positive for the stimulant nikethamide at the Munich Open in Germany last April and will not return to action until February 1, 2014.
The 24-year-old, who has had the ban backdated to May 1 this year, told an independent tribunal that the nikethamide had entered his system after he took Coramine glucose tablets which had been purchased on his behalf.
Cilic will now appeal against the decision by taking his case to the Court of Arbitration for Sport, claiming he was not aware that the Coramine tablets contained a banned substance.
"The substance in question originated from a glucose tablet purchased at a pharmacy in France," Cilic said in a statement Monday.
"Unbeknownst to me, the glucose tablets contained a substance that is banned in competition.
"I wish to emphasize that I have never knowingly or deliberately taken any banned substances in my life and that I am opposed to any use of performance enhancing substances in sport."
The tribunal accepted that Cilic "did not intend to enhance his performance" by taking the substance, and ruled he will instead serve a reduced ban of nine months.
Cilic, who has not competed since withdrawing from Wimbledon citing a knee injury, has had his results at the Munich Open expunged and has forfeited both the prize money and rankings points from the event.
The Croatian reached a career high of No.9 in the world in 2010 after reaching the semifinals of that year's Australian Open.
Cilic is the fourth tennis player to be hit with a ban for drug violations in 2013.
Serbia's Viktor Troicki was suspended by the ITF for 18 months in July after being found guilty of failing to provide a blood sample during April's Monte Carlo's Masters.
But Serbian Troicki has vowed to appeal the decision after alleging the doctor conducting the blood test allowed him to miss the procedure.
In May, Brazil's Fernando Romboli tested positive for diuretics, furosemide and hydrochlorothiazide which resulted in him being handed an eight-and-a-half month ban.
In February, Czech player Barbora Zahlavova Strycova received a six month ban after testing positive for sibutramine, a substance which is often found in weight loss products.
The ITF has stepped up its fight against drugs cheats since announcing its plan to introduce biological passports in March.
Each player will have an individual electronic biological profile and be tested more regularly to monitor their levels and alert the authorities to possible drug use.