The decision to default Novak Djokovic from the US Open for hitting a linesperson with the ball was the correct call, according to Billie Jean King.

World number one Djokovic was disqualified during his fourth-round match against Pablo Carreno Busta after dropping serve to trail 6-5 on Sunday.

As he made his way back towards his chair, the Serbian hit a ball towards the back of the court and it connected with a line judge, who audibly gasped for air.

Djokovic went over to assist the woman but, following a lengthy conversation with the match officials, was defaulted for "intentionally hitting a ball dangerously or recklessly within the court or hitting a ball with negligent disregard of the consequences".

The 17-time major champion was the favourite to win the grand slam in New York and his exit leaves the men's singles draw wide open.

King wrote on Twitter: "Here are my thoughts on the Novak Djokovic default.

"First, I hope the line judge is okay. The rule is the rule. It is unfortunate for everyone involved, but in this specific situation the default was the right call."

Prior to seeing Carreno Busta break his serve, Djokovic received treatment on his shoulder have failed to convert any of the three set points he engineered in the 10th game.