The head of a Hungarian anti-racism group said far-right soccer fans shouted "Sieg Heil" and attacked him, breaking his nose days before the country is due to host the World Jewish Congress.
Ferenc Orosz, chairman of the Raoul Wallenberg Association, told Reuters he was assaulted after arguing with a group of supporters chanting the Nazi slogan at a match between the Hungarian teams Videoton and Ferencvaros in Budapest on Sunday.
The campaign group was formed in tribute to Swedish diplomat Raoul Wallenberg who saved the lives of thousands of Hungarian Jews during the Holocaust.
Jewish and rights groups say anti-Semitism remains a significant problem in the central European country - a leader of its far-right Jobbik party called for lists of prominent Jews to be drawn up to protect national security in November.
Orosz said he tried to silence the supporters at the game in the city's Ferenc Puskas Stadium. Some members of the group called him a "Jewish communist" and he was approached by two men afterwards, one of whom hit him.
"Since Jobbik got into parliament (in 2010), hate speech has gained a lot more ground," Orosz told Reuters on the sidelines of a conference about hate speech on Monday. Far-right campaigners say they are planning to stage a rally against Bolshevism and Zionism in Budapest on Saturday, the evening before the start of the meeting of the World Jewish Congress, which represents Jewish communities around the world.
The Hungarian prime minister's chief of staff, Janos Lazar, said earlier on Monday the interior ministry had been told to stop any offensive demonstrations or activity ahead of the three-day meeting in Budapest.
More than 500,000 Hungarian Jews were killed in the Holocaust after Hungary sided with the Nazis in World War Two.