Having taken a 2-1 lead into the fourth set against Jannik Sinner, Zverev was serving in the fifth game when he suddenly stopped and approached the chair umpire.
“He just said the most famous Hitler phrase there is in this world, it’s unacceptable,” Zverev said, before the umpire addressed the crowd in the stands behind him.
The fan was then booed as he was escorted out by security.
“He started singing the anthem of Hitler that was back in the day. It was Deutschland Über alles and it was a bit too much,” Zverev said after the match.
The German star beat Sinner 6-4, 3-6, 6-2, 4-6, 6-3 in their fourth-round clash.