World No. 1 Novak Djokovic hit back at criticism from Nick Kyrgios on Sunday, saying he has little respect for the Australian firebrand off the court.

"My respect goes to him for the tennis he's playing. I think he's a very talented guy," Djokovic told reporters.

"He's got a big game. He has proven that he has a quality to beat any player really in the world in the past. Off the court, I don't have much respect for him, to be honest. That's where I'll close it. I really don't have any further comments for him, his own comments for me or anything else he's trying to do," he added.

Kyrgios, a long-time critic of Djokovic, labelled him a "tool" on social media last month after the Serb sent Australian Open organisers a list of requests from players seeking to have quarantine restrictions eased during their mandatory two-week isolation.

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Defending champion Djokovic starts his bid for a record-extending ninth Australian Open title, as well as an 18th Grand Slam crown, on Monday against unseeded Frenchman Jeremy Chardy in the evening session at Rod Laver Arena.

He was in fine form during the ATP Cup, though Serbia's title defence ended in the quarterfinals with a doubles defeat to Germany.