Australian player Max Purcell was booed off the court in New York after suddenly quitting his US Open match with no explanation.

Purcell had taken No.14 seed and hometown hero Tommy Paul deep in their first set, which went to the American 7-5.

But Purcell then inexplicably capitulated and the 26-year-old from Sydney lost seven straight games.

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Paul won the second set 6-0 and was up 1-0 in the third when Purcell called him to the net and shook his hand.

The crowd booed as Purcell packed his bag and walked off, with even his opponent left wondering what happened.

“It’s unfortunate,” Paul said.

“The first set was super entertaining tennis, I love the way he plays.

“I think I saw a little bit (of a potential injury) there at the end of the second, and obviously I wanted to finish, I was playing really well… it’s unfortunate.”

Purcell had beaten fellow Aussie Aleksander Vukic in round one to book his meeting with Paul.

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Australian tennis great Jelena Dokic was shocked to see Purcell walk off the court without asking for a medical timeout beforehand.

“This is not usual, because usually you would call a fitness trainer and consult with them, or a physio,” Dokic told Nine.

“So a little bit unusual he just stopped there, had a little bit of a conversation with Tommy Paul, (he) didn’t say too much.

“Maybe it’s something that we didn’t see, let’s hope he is OK.

“Max actually played a great first set, it was really tight, so let’s hope it is nothing too serious.”

Paul now faces Gabriel Diallo in round three.