Nazi-sympathising singer's huge gig to paralyse Zagreb
A dozen hospitals have been put on alert to brace for a surge in demand during the Thompson concert on Saturday, while thousands of police will be deployed to manage the influx into a city already hosting summer tourists.
A field hospital with 200 beds will also be set up near the racecourse venue and fans have been warned to prepare for summer heat.
Marko Perkovic, known by his stage name Thompson, has been banned from performing in several countries due to his sympathies with Croatia's World War II fascist Ustasha regime.
Ustasha symbols are common at Thompson concerts, and he begins one of the most popular songs by screaming a fascist slogan infamously used by the Nazi-allied regime.
'People adore him'
The concert sold out in just a few days in April, with a third of his fans under 28, according to the ticketing platform Entrio. Police said there would be at least 450,000 people at Croatia's biggest concert.
"People adore him, due to his patriotic songs and affection for Croatia," 22-year-old Nikola, who did not give his family name, told AFP ahead of the concert.
The student ignores the Ustasha shouts from Thompson and said it just reflects the "wartime" era in which the song was recorded.
"I was not even born when it was released."
A folk-rock icon of Croatia's right-wing, Thompson first became popular for his nationalist songs in the 1990s during the country's war of independence.
But his manager, Zdravko Barisic, told local media that it was "inappropriate" to accuse him of Ustasha sympathies and that he was hosting a "concert, not a political rally".
Zagreb's left-wing mayor, Tomislav Tomasevic, rejected earlier calls to ban the performance, saying they were "counter-productive".
'Patriotic charge'
In recent years, Croatia has seen a growing tolerance for its pro-Nazi past and critics accuse authorities of failing to sanction the use of Ustasha emblems.
The Ustasha persecuted and killed hundreds of thousands of Serbs, Jews, anti-fascist Croatians, Roma and others in concentration camps during World War II.
Although the Ustasha's so-called Independent State of Croatia was a Nazi puppet, their modern sympathisers see the regime's leaders as the nation's founding fathers.
The Simon Wiesenthal Center, a leading Jewish human rights group, had accused Thompson of glorifying genocide in his lyrics and said the display of Ustasha insignia at his concerts was "neither a coincidence nor a mistake".
But historian Hrvoje Klasic told AFP that the singer's popularity does not reflect an increasing support for far-right movements in mainstream society.
The vast majority of fans perceive Thompson as a "patriot, presenting traditional values like homeland, religion, family", Klasic told AFP.
"Croatian society traditionally leans slightly to the right, with a patriotic charge."
The last parliamentary elections, however, saw the Homeland Movement (DP), known for its nationalist and anti-migrant rhetoric, join the coalition government.