Police on Saturday detained controversial Dinamo Zagreb chief Zdravko Mamic and his younger brother Zoran, the Croatian champions' coach, on suspicion of multi-million-euro bribery and tax evasion, the club said.

The two decided to return from neighbouring Slovenia -- where they were with the players preparing for next season -- to be questioned by anti-corruption investigators in order "to prove their innocence," a club statement said.

The club added that they were detained by Croatian police at the border and that they were accompanied by their defence lawyers.

The national anti-graft USKOK bureau said Friday that the two, along with a top official at the Croatian Football Federation (HNS) and a tax inspector, were suspected of giving and receiving bribes, tax evasion and other offences.

The alleged offences cost Dinamo Zagreb almost 118 million kunas ($17.3m, £11.1m, 15.5m euros) and the state some 12 million kunas. The suspected criminal offences had been taking place since 2008, an USKOK statement said.

Meanwhile, Damir Vrbanovic, the HNS executive president and a former Dinamo director, was questioned by anti-graft prosecutors on Friday along with the tax inspector.

A Zagreb court was to decide whether to accept the anti-graft bureau's request to keep the four in custody.

On Thursday, policed searched the homes of the Mamic brothers as well as the premises of Dinamo and the HNS.

But Zdravko Mamic, considered the most influential man in Croatian football, had labelled the allegations against him "absolutely pointless and constructed."

The 55-year-old Dinamo executive president said they were politically motivated and accused Prime Minister Zoran Milanovic of being behind them.

Mamic is a controversial figure well known for his outspoken behaviour and threatening journalists.

Last year he was convicted of slander and ordered to pay 17,000 euros to a lawyer representing Brazil-born Croatian striker Eduardo da Silva. In 2014, he was acquitted of inciting hatred with a slur against an ethnic Serb minister.