NOVAK DJOKOVIC 鈥 REUTERS

NOVAK DJOKOVIC expressed his frustration at being 鈥渒ept in the dark鈥 about world number one Jannik Sinner鈥檚 doping case, saying in Brisbane on Sunday that it was not a good look for tennis.

Anti-doping authorities said in August Sinner twice tested positive in March for the anabolic androgenic steroid clostebol and was cleared of wrongdoing by an independent tribunal that accepted his explanation of unintentional contamination.

The 23-year-old Italian faces a potential ban of up to two years after the World Anti-Doping Agency appealed that decision at the Court of Arbitration for Sport.

鈥淚t鈥檚 not a good image and not a good look for our sport,鈥 Djokovic told reporters ahead of the Brisbane International.

鈥淵ou don鈥檛 want to see that. I believe that in the last 20-plus years that I鈥檝e been playing on the professional tour that we鈥檝e been one of the cleanest sports. I鈥檒l keep believing in that clean sport.

鈥淚鈥檓 just questioning the way the system works, really, and why certain players are not treated the same as other players.鈥

Sinner鈥檚 was not the only recent high-profile case in the sport as world number two Iga Swiatek accepted a one-month ban that ended on Dec. 4 after a positive test for trimetazidine, which she said was due to contamination of her sleep medication.

The International Tennis Integrity Agency maintains that all doping cases are dealt with based on facts and evidence and not a player鈥檚 name, ranking or nationality, but has not been able to fend off allegations of double standards.

鈥淭he issue is the inconsistency and the transparency. We鈥檝e been kept in the dark with Jannik鈥檚 case,鈥 Djokovic added.

鈥淚鈥檓 not questioning whether he took the banned substance intentionally or not. I believe in a clean sport, I believe that the player will do everything possible to be playing fair.

鈥淚鈥檝e known Jannik since he was very young. He doesn鈥檛 strike me as somebody who would do such a thing. But I鈥檝e been really frustrated as (have) most of the other players to see that we鈥檝e been kept in the dark for five months.鈥

Outspoken Australian Nick Kyrgios said the cases involving Sinner and Swiatek were 鈥渄isgusting鈥 for the sport and slammed authorities over what he saw as lenient treatment. 鈥 Reuters