Serbia's Viktor Troicki, who was banned for 18 months by the International Tennis Federation (ITF) for flouting doping rules, on Friday denied any wrongdoing and said he would appeal the sanction.
The 27-year-old was found guilty of failing to provide a blood sample during a drugs test at the Monte Carlo Masters in April.
"I am destroyed and exhausted... This enormous sanction makes me speechless," Troicki said in a statement at his official web site www.viktortroicki.com.
Troicki said he would appeal the ITF decision.
"I put my trust in the Court of Arbitration of Sports in Lausanne, I really hope they will look for the truth and find it, which is only one."
Troicki said that it was the doping control officer (DCO) who had allowed him go without giving a blood sample because he felt "awfully bad" that day.
"The doctor in charge of the testing told me that I looked very pale and ill, and that I could skip the test if I wrote an explanation letter to ITF about it. She dictated the letter to me and let me go without giving blood. She was very helpful and understanding.
"Now I am being charged for refusing to undergo a blood test without justification. This is a real nightmare," Troicki said.
However, according to the ITF, an independent "tribunal concluded that the DCO told Mr Troicki that she could not advise him as to whether his reason for not providing a blood sample was valid, and that no such assurances were given by her."
Troicki, who is currently at 53 in the world, reached a career high 12 in 2011 and has won $4.5 million (3.4 million euros) in prize money.
In 2010 he won the decisive fifth and final rubber against France as Serbia claimed the Davis Cup for the first time.