Beijing: World number one Novak Djokovic has launched a vigorous defence of childhood friend and Davis Cup colleague Viktor Troicki.

The former world No 12 has been banned for 18 months until January 2015 by the International Tennis Federation (ITF) for failing to provide a blood sample during a mandatory drugs test during the Monte Carlo Masters in mid-April.

But Djokovic was eager to back his friend, whom he has known since they were eight years old, and revealed he had signed a petition calling for new rules regarding the way the doping process works.

“The whole case around Viktor is just very unfair towards him. I believe that he’s innocent. He hasn’t been charged for being positive on any kind of substance. He was just accused of failing to provide the blood test that day,” Djokovic said.

“We grew up together. He’s one of my best friends. There is no doubt in my mind that he’s innocent. I supported him from the first moment. I think the case is coming up for hearing [in Lausanne] on October 9. I hope that he’s going to be discharged and he’s going to be able to play, because he’s definitely not guilty.”

The world number one said he was baffled as to why Troicki had been suspended. “I don’t see why they’re keeping him suspended. For what? For failing to provide the blood test,” he said.

“I leave the authorities to deal with it, but I’m confident that he’s going to come back on the tour, hopefully already in the next couple weeks, and he’s going to be with us in Davis Cup final.

“So the reason why I was the first one to write a petition for the rule change is to try to spread the awareness to people around that obviously there is a little bit more politics involved. It’s unfortunate that it all comes down to Viktor’s case, because it shouldn’t be like that. He’s not [tested] positive for anything and he’s absolutely innocent.”