On the eve of his return to the court, Novak Djokovic has weighed in on tennis’s high-profile doping cases and criticized what he perceives as double standards in the sport. The former world No. 1, who is chasing a record 25th Grand Slam title at next month’s Australian Open, expressed his frustration Sunday at being “kept in the dark” regarding top-ranked Jannik Sinner’s doping case. Djokovic is the top seed in the Brisbane International this week, making his first appearance at the event since 2009.