The world No 1 had just dropped his serve to trail opponent Pablo Carreno Busta 6-5 in the opening set of their fourth-round match on Arthur Ashe Stadium.
He hit a ball behind him in disappointment and it struck a female line judge. After the ball was struck, it was promptly evident that the lady was harmed and the Serbian surged over to keep an eye on her condition
Djokovic had not lost this season, enjoying a 26-match winning run, and had secured his 17th Grand Slam singles title at the Australia Open.He was favorite to make it 18 in New York.