Vienna police are probing a claim by a rabbi that a football fan insulted him and gave the Hitler salute, while police stood by and did nothing.
"A complaint by a Jewish citizen is being studied by our complaints bureau," the police told AFP.
Rabbi Schlomo Hoffmeister said a football fan had shouted: "Get lost, you dirty Jew! Jews, get out! Heil Hitler!" and gave a Nazi salute when he saw him last Thursday in Vienna's city center.
The incident took place on a square where football fans had gathered before a Europa League play-off between Rapid Vienna and Greek club PAOK Salonica.
Hoffmeister complained to police officers standing nearby, but he said they did not intervene.
"We are currently questioning the police unit that may have witnessed the incident," police spokesperson Roman Hahslinger said Monday.
The suspected offender was believed to be a PAOK fan, he added.
The Simon Wiesenthal Center meanwhile said it had written to Austria's interior minister to protest the affair, adding that it was "most shocking... that police witnesses refused to intervene."
Austria's Jewish community (IKG) added it saw "a great threat in the passivity of police officers towards anti-Semitic attacks."
Last Thursday's UEFA Europa League match between Rapid Vienna and PAOK Salonica was held under tight security after a game in Greece a week earlier had deteriorated into fighting between the two sides.