Serbia's former World No 12 Viktor Troicki has been handed an 18-month suspension by the International Tennis Federation (ITF) after violating doping regulations.
The ITF said on Thursday that the 27-year-old, a Davis Cup teammate of world number one Novak Djokovic, had been found guilty of "refusing or failing without compelling justification to submit to sample collection."
Troicki, who is now 53rd in the world rankings, is one of the most high-profile players to break doping rules in tennis.
In a statement the ITF said Troicki had been notified on April 15 that he had been selected to provide a urine sample and a blood sample in association with his participation at the Monte Carlo Masters event.
"(He) provided a urine sample, but did not provide a blood sample. He asserted to an independent tribunal that he was assured by the Doping Control Officer (DCO) that it would be acceptable not to provide a sample on account of him feeling unwell that day," the ITF's statement read.
"However, the 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."
The ITF said Troicki's actions constituted "a failure and a refusal" to provide a blood sample, and that his explanation for not doing so was not "compelling".
Troicki, who the tribunal heard was under stress at the time, will be suspended until January 24, 2015.
Image: Viktor Troicki of Serbia
Photograph: Dennis Grombkowski/Getty Images