The world tennis number two Novak Djokovic says he has lost all trust in the anti-doping programme in tennis.
Djokovic fears he could become a victim of its negligence after fellow Serb Victor Troicki failed to have his doping ban overturned.
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 against an 18-month ban imposed by the International Tennis Federation 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 a year by CAS.
Djokovic says the ruling proves again that World Anti Doping Agency's system isn't working and he doesn't trust it.
Troicki has denied any wrongdoing and based his appeal on his belief he'd been told by a doping control officer he wouldn't be committing a doping violation if he didn't provide a blood sample.
Troicki says he he felt unwell on the day of the test and that his phobia about needles would make him feel even worse.
The CAS hearing accepted there had been confusion between the doping control officer and Troicki over whether he could be excused the blood test.