Serbia's Football Association president Slavisa Kokeza was questioned by police on Sunday in connection with recent arrests of several members of a football fan group accused of murder, kidnapping and drug trafficking.
Serbian media said Kokeza was quizzed over his links to leaders of the Partizan Belgrade supporters' group who were arrested earlier this month in what officials say is a major crackdown against football's links with organised crime.
Kokeza reportedly refused to answer questions and also refused a lie-detector test during the questioning.
Details from the police investigation leaked to the media include alleged killings by group members of their rivals, including decapitations and torture in a special "bunker" at the Partizan stadium in the Serbian capital.
Populist Serbian President Aleksandar Vucic, who has often boasted about his youth as a radical supporter of Partizan's rival Red Star Belgrade, said on Saturday that some of the "shocking" details of the investigation will be made public next week and that children will be warned not to watch.
Vucic has suggested that the fan group members wanted to kill him although his 23-year-old son was frequently photographed with its members in recent years.
Vucic's opponents have said the arrests appear to have been made for show because it is widely accepted that the regime has for years maintained close links with football group leaders.
Serbia has a history of tolerating hooliganism that often resulted in violence and outbursts of nationalism at stadiums. During the Balkan wars in the 1990s, many of them joined notorious paramilitary groups linked to war crimes against other national groups in the former Yugoslavia.
Last week, European football governing body UEFA opened a disciplinary investigation after AC Milan's Zlatan Ibrahimovic was subjected to racist abuse during a Europa League match against Red Star in Belgrade.
With the return of nationalists to power in Serbia nine years ago, far-right football supporters were often seen at pro-government rallies promoting a nationalist political agenda. In exchange, analysts have said, the hooligans have been allowed to pursue their illegal business activities.
More than a dozen prominent figures from the country's football supporters' groups have been murdered in recent years. Most have perished in gangland-style killings.