Losing the match, Djokovic, apparently frustrated, hit the ball with the tennis racket without even looking, hitting the female judge who was behind his back.

17-time Grand Slam champion Novak Djokovic has been disqualified from the US Open 4th round for inappropriate behaviour.

Footage from the scene shows Djokovic hitting a line judge aggressively with a tennis ball, after which she falls to the ground reaching for her neck. Djokovic looks shocked at first before he heads towards the woman.

Djokovic was trailing 6:5 in the opening set against Spain's Pablo Carreno Busta.

After the incident happened, Djokovic had a discussion with officials on court, then the chair umpire announced the default. According to the New York Times, Djokovic argued against his disqualification, saying that the judge did not have to go to hospital after being hit. However, later, Djokovic said he was "extremely sorry", adding that the situation left him "really sad and empty".

The United States Tennis Association (USTA) said Djokovic will lose all his ranking points and will be fined prize money earned in the tournament, in addition to other fines related to the incident.

Djokovic's disqualification means a maiden grand slam champion in men's singles will appear on the US Open for the first time since 2014.