A fan was ejected from the US Open after being accused by Alexander Zverev of using "the most famous Hitler phrase there is in this world".
Organisers removed the fan from Arthur Ashe Stadium on Tuesday after a complaint from German 12th seed Zverev.
The 26-year-old heard a remark from a spectator in the crowd during his win over Jannik Sinner.
Zverev was serving in the fourth set when he stopped and approached chair umpire James Keothavong.
"This is unacceptable. This is unbelievable," a furious Zverev told the umpire.
Keothavong immediately turned around and asked the man to identify himself but he did not come forward.