Novak Djokovic apologised for hitting a linesperson and being disqualified at the US Open, saying he was feeling "really sad and empty".

World number one Djokovic was stunningly disqualified after hitting a linesperson with a ball during his last-16 clash with Pablo Carreno Busta.

The Serbian, who skipped his news conference, later released a statement apologising, saying he would learn from his actions.

"This whole situation has left me really sad and empty," Djokovic wrote in a statement posted on social media.

"I checked on the line person and the tournament told me that thank God she is feeling ok. I'm extremely sorry to have caused her such stress. So unintended. So wrong. I'm not disclosing her name to respect her privacy.

"As for the disqualification, I need to go back within and work on my disappointment and turn this all into a lesson for my growth and evolution as a player and human being.

"I apologise to the @usopen tournament and everyone associated for my behaviour. I'm very grateful to my team and family for being my rock support, and my fans for always being there with me. Thank you and I'm so sorry."

Favourite to win the US Open and his 18th grand slam title, Djokovic's exit means there will be a first-time major winner in the men's draw in New York.