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 number 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.
Elena Gorodilova, the doping control officer at the centre of the case, disputes Troicki's version of events in evidence supplied to CAS, saying whether or not he was entitled to skip the blood test was "not her decision to make".
In a statement, Troicki said his dream of being a top player had been taken away and Djokovic was full of sympathy for his compatriot.
"So first of all he's not positive on any banned substance," Djokovic, who initially brought a prepared script to the news conference, said.
"I'm not saying that it's completely not his fault, but the way it was is that he had a medical pass where he was fainting, if he feels bad when he provides the blood test.
"He asked if it's possible to avoid providing blood test that day and he would come the next day - not because he wanted to hide anything, he just felt bad.
"She did not clearly present him all the severe consequences that he will have if he avoids that. She told him that he needs to write a report and that he will be just fine.
"And because of her negligence and because of her unprofessionalism, he is now off the tour for one year.
"And now it makes me nervous as a player, you know, to do any kind of test."
ITF President Francesco Ricci Bitti said his organisation was committed to protecting "the integrity of the game of tennis" and defended the doping control officers.
"We respect the ruling of the Court of Arbitration for Sport, who confirmed the decision of the Independent Tribunal that Viktor Troicki is guilty of an anti-doping violation, although they reduced the penalty to one year," he said.
"What is harder to accept is criticism of Doping Control Officers who perform a difficult role.
"Finally, separate from this decision, we should all remember that exactly one year ago anti-doping programmes around the world were under scrutiny.
"This reinforced the need to be vigilant and apply the rules strictly, something that we and our partners in the Tennis Anti-Doping Programme strive to do to keep our sport clean."
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