World No.1 Novak Djokovic has been disqualified from the US Open after hitting a line judge with the ball after a point during his fourth round match against Spain’s Pablo Carreno Busta.

It was a stunning end to Djokovic’s bid for an 18th grand slam title and his 26-0 start to this season.

The top seed had just lost a game to Carreno Busta, to fall behind 6-5 in the first set.

As he walked to the sideline for the changeover, Djokovic smacked a ball behind him.

The ball hit a female line judge, who dropped to her knees at the back of the court.

After a discussion of several minutes with officials on court, Djokovic walked over to shake hands with Carreno Busta, and the default was announced.

“In accordance with the grand slam rulebook, following his actions of intentionally hitting a ball dangerously or recklessly within the court or hitting a ball with negligent disregard of the consequences, the US Open tournament referee defaulted Novak Djokovic from the 2020 US Open,” a US Tennis Association statement said.

“Because he was defaulted Djokovic will lose all ranking points earned at the US Open and will be fined the prize money won at the tournament in addition to any or all fines levied with respect to the offending incident.”

There was no question Djokovic did not intend to hit the line judge, and the ball was not hit particularly hard, but it was clear immediately that the woman was hurt, with the Serbian rushing over to check on her condition.

He pleaded his case at length before accepting his fate, collecting his racquets and walking off the court.

The decision will send shockwaves through the sport.

Djokovic won his 17th slam singles title in Australia and was an overwhelming favourite to make it 18 in New York having not lost a match all season.