Novak Djokovic says he has lost all trust in the anti-doping programme in tennis and fears he could become a victim of its “negligence” after fellow Serb Victor Troicki failed to have his doping ban overturned on Tuesday.

Djokovic beat Roger Federer in his opening match at the ATP World Tour Finals but his joy was overshadowed by news that Troicki’s appeal to the Court of Arbitration for Sport (CAS) against an 18-month ban handed out by the International Tennis Federation (ITF) in July had only been partly successful.

Troicki, who was banned after failing to provide a blood sample at the Monte Carlo Masters in April, had his sanction reduced to 12 months by CAS, ruling him out until next July.

After a few questions about Tuesday’s Group B victory, the world number two was asked for his thoughts on Troicki and produced a stinging monologue lasting several minutes.

“First of all, Viktor is a very good friend of mine,” an emotional Djokovic told a late-night news conference at London’s O2 Arena.

“It’s very bad news that we got for him, and for me, for all of us who are close to him.

“But I think it’s just not bad news for him, it proves again that this system of WADA and anti-doping agency does not work.

“I don’t have trust in them anymore. I don’t have trust in what’s going on.

“I don’t know if tomorrow the representative, the DCOs (doping control officer) who are representatives of WADA there at the tournaments, because of their unprofessionalism, because of their negligence, because of their inability to explain the rules in a proper way, I don’t know if they’re going to misplace the test that I have or anything worse than that.”

Troicki has denied any wrongdoing and based his appeal on his belief that he had been told by a doping control officer at the Monte Carlo tournament he would not be committing a doping violation if he did not provide a blood sample, providing he contacted the ITF to explain the situation.

The 27-year-old told an ITF independent tribunal that he had felt unwell on the day of the test following his early defeat and that his phobia about needles would make him feel even worse. He subsequently wrote a letter to the ITF’s anti-doping department to explain his reasons for refusing to give a sample.

The CAS hearing agreed that former world no. 12 Troicki, who won the decisive rubber for Serbia in the 2010 Davis Cup final, was not “significantly” at fault and accepted there had been “confusion” between the doping control officer and Troicki over whether he could be excused the blood test.

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