Sandi Sola, the head of Croatia's Handball Federation, was arrested on Thursday under suspicion of embezzling millions of euros from a local bank along with seven other people, including his family members.
Sola, a former head of the Karlovacka bank's management board, was detained on the border with Serbia on his way back to Croatia.
He was immediately questioned by anti-graft prosecutors and denied all the charges, his lawyer Ante Madunic told reporters.
The others, including his mother Marija Sola, a known businesswoman who is the prime suspect, and two brothers, were arrested on Wednesday.
The group is suspected of abuse of power and embezzlement of at least 37.5 million kunas (five million euros, $6 million) from the bank, and another 46.9 million kunas from a local company, a police statement said.
According to local media reports, Sola's family holds a majority stake in the bank.
Sola has headed the federation since 2008.
Croatia, a double gold Olympic medallist, took third at this year's Handball World Championship in Spain.