Novak Djokovic, one of the world’s best tennis players, appeared stunned when he was defaulted from his fourth-round match at the U.S. Open in New York on Sunday after accidentally hit a line judge in the neck with a tennis ball.

2020 US OPEN: WHAT TO KNOW ABOUT MEN'S SINGLES TOURNAMENT

The incident occurred inside Arthur Ashe Stadium after the top-seed player lost a game to Pablo Carreno Busta. Djokovic hit the ball behind him and hit the line judge, who dropped to the floor while holding her neck.

Djokovic later apologized over the incident,  saying he is “extremely sorry for creating” such stress for the line judge.

“This whole situation has left me really sad and empty,” the 33-year-old said. He said he checked to see how she was feeling and told she was doing well. He said it was “so unintended” and “so wrong.”

His disqualification from the tournament sparked debate online over whether the chair umpire and other tournament officials were fair with the decision. Djokovic could be heard on the court saying, “It’s tough for you, whatever call you make, I understand.” Tennis.com reported that these tournaments are “fairly inflexible in such situations.”

Rennae Stubbs, a six-time Grand Slam champion, took to Twitter late Sunday and posted, “LET ME SAY THIS LOUDLY! Anyone who blames the lines lady for the default of Novak…STOP! The lady had  NOTHING to do with the default! Repeat! Nothing!!! OK!!!! IT’S A RULE! There was NOOOOO WIGGLE ROOM ON THIS! NONE!!”

SERENA WILLIAMS SETS UP US OPEN SHOWDOWN VS. SLOANE STEPHENS

New9 pointed out a time during the 2016 French Open when Djokovic flung his racket and just barely missed another linesperson.

GET THE FOX NEWS APP

That same year, a journalist asked him about those kinds of incidents and whether or not he was concerned that something like that could cost him in the future and he dismissed the question.

"I think that it was bad luck, no? You cannot do this, but of course I think that Novak never, never wants to hit the line umpire," Carreno Busta said.

The Associated Press contributed to this report