Organisers removed the fan from the Arthur Ashe Stadium early on Tuesday after the German 12th seed approached chair umpire James Keothavong during the fourth set to alert him of the situation.

"He just said the most famous Hitler phrase there is in this world," Zverev said.

"It's not acceptable."

Keothavong quickly turned around, asking the fan to identify himself before asking fans to be respectful to both athletes.

The fan was removed by security during a changeover shortly after, as the crowd cheered.

"He started singing the anthem of Hitler that was back in the day," Zverev said.

"It was Deutschland über alles and it was a bit too much.

"I think he was getting involved in the match for a long time, though. I don’t mind it, I love when fans are loud, I love when fans are emotional.

"But I think me being German and not really proud of that history, it’s not really a great thing to do and I think him sitting in one of the front rows, I think a lot of people heard it.

"So if I just don’t react, I think it’s bad from my side."

The opening lines of the German national anthem, "Deutschland, Deutschland, über alles, über alles in der Welt", has been dropped for many years due to its links with Hitler's fascist Nazi regime.

US Tennis Association spokesman Chris Widmaier said that the remarks against Zverev was "disparaging".

Zverev went on to win the match 6-4, 3-6, 6-2, 4-6, 6-3 in four hours and 41 minutes - the longest match of this year's US Open - and is set to face Spanish defending champion Carlos Alcaraz in the quarter-finals.