Novak Djokovic says it was a "a very awkward situation" when a ball flew off his racquet into a line judge's face during a French Open fourth-round win.

This time - in a straight-set win over Karen Khachanov - there was no chance of a default as the ball was still in play and it was not a dangerous action.

"I hope he's fine," Djokovic said.

"He dealt with it in a strong and brave way. But it was a hit because I was very close."

World number one Djokovic was disqualified in his US Open fourth-round match against Spain's Pablo Carreno Busta when he accidentally hit a line judge in her throat with the stray ball after losing serve in the first set.

This is his first Grand Slam since that controversy and it was another anxious moment for him in the first set when a Khachanov return flew off the frame of his racquet towards the side of the line judge's face.

Thankfully, the man was unhurt and there was none of the drama that followed the incident in New York.

"It was very awkward deja vu. I'm actually trying to find the lines person and see if he's okay because I saw he had a little bit of a bruise, like redness, in that place in the head where the ball hit him," the top seed said.

"Obviously because of what happened in New York, people I guess are going to make the story out of this.

"It has happened to me and to many other players in the last 15 years that I've been on the tour.

"I've seen it a lot when the ball ricochets from the racquet and the frame, hits someone in the stands, or someone that is close to you or a line umpire."

The Serb will face another reminder of what happened in New York when he lines up against Carreno Busta again in the quarter-finals in Paris.

The Spanish 17th seed beat German qualifier Daniel Altmaier 6-2 7-5 6-2 on Monday.

Djokovic's 6-4 6-3 6-3 win against Russian 15th seed Khachanov means he has still not lost a completed match this year, with his only defeat in 36 matches coming when he was defaulted at Flushing Meadows.