Novak Djokovic argued that the doping case involving Jannik Sinner is 'not helping tennis at all'. Sinner twice tested positive for a banned substance earlier this year but was allowed to play by an independent tribunal. He went on to win the US Open but now the World Anti-Doping Agency have appealed against the decision to clear Sinner. Speaking ahead of this week's Shanghai Masters, where Sinner is the top seed, Djokovic said that tennis has 'a system that is not working well', adding: 'Even people who are not following our sport, are realising there are way too many inconsistencies and way too many governing bodies involved'.