Dick Pound, the former chief of the World Anti-Doping Agency, has criticized Novak Djokovic's comments about the amount of doping in the sport.

"That's a Lance Armstrong approach. 'I never tested positive therefore I am clean.' Wrong," Pound told STV.

"As long as there is no proof that somebody is doping, the sport is clean," Djokovic was quoted saying at the Laureus World Sport Awards, reacting to Andy Murray's statements that he has been suspicious of players on tour and wants tougher anti-doping efforts.

"I think it all comes down to anti-doping agencies, governing bodies—they need to come out with proof, if they don't it's only rumors," Djokovic also said.

Pound, known for his strident stance against doping and also for his controversial statements on its prevalence in sport, added that the reluctance of sporting bodies to catch offenders is also an issue.

"Let's assume it's double digits and let's be really charitable and say it is only 10 percent," he said. "Our level of positives is 2 percent. The science is pretty robust and the system is good for whatever it does. It's the people that don't want it to work."

Murray, meanwhile, said he planned to keep speaking up about his concerns, but has a good relationship with Djokovic. Boris Becker, Djokovic's coach, had also criticized Murray.

"I've spoken to Boris and Novak and we're all good," Murray said. "I'm practicing with Novak next week in Madrid.

"It's a topic that's always difficult for athletes to discuss these days but we have to try and do our best. All I want is to try and make sure tennis is as clean, a sport, as possible—it's very difficult to keep a sport that way these days."