Massive flags, banners and chants of "Dinamo, Dinamo" were a strange sight at Salata, a recreational sports centre in the middle of Zagreb.

On a warm September evening, thousands filled the stands surrounding a concrete outdoor playground and watched men in blue shirts play a sport awkwardly named 'futsal'.

Among the messages displayed in the crowd were: "Dinamo - to smo mi" (Dinamo - that's us) and "Jedan clan, jedan glas" (One member, one vote).

A few days later, the 'real' Dinamo Zagreb played a home game against Istra in the league and official figures said the attendance was 1100. It was, in fact, much lower, as anyone who was there can testify: the stands of the 38,000 Maksimir stadium stood eerily empty. There were no chants, flags or banners.

This is GNK Dinamo, the perennial Croatian champion and - without any competition - the biggest club in the nation's capital, where almost a million people live. The one at Salata is the recently founded MNK Futsal Dinamo, about to compete in 2nd (futsal) division. MNK is owned and run by its members; GNK is run by two brothers who don't even own it.

The chief executive of the 'big' Dinamo is the controversial Zdravko Mamic, also routinely described as the 'Puppet Master' for his massive influence in the national football federation. Upon seizing power at the club, he proclaimed that the club would be champions for the next decade. Since then, they've amassed nine league titles in a row and are currently topping the table in their 10th season with Mamic in charge. They also regularly play in Europe, buy and sell players for sums other Croatian clubs can only dream about and have established a youth academy which is among the most productive in Europe.

And yet the club has managed to estrange its fans, who would now rather go to watch futsal. Their ultras, the notorious Bad Blue Boys, have left their North stand symbolically empty; when they gather for some games in the East, there are more chants that are anti-Mamic than those actually supportive of the team.

For European games, Dinamo give away tickets on a massive scale, mostly to schoolchildren: in this manner, they managed to gather 10,000 for their Europa League match against Astra Giurgiu.

Legally a citizens' association that receives public funding, the club is supposed to offer all of its members the right to elect and be elected. Instead it's being run as a family business, with Zdravko Mamic and his lawyers using bureaucratic trickery to prevent free elections to the board. His brother Zoran, previously a professional player, acts in dual role as both sporting director and manager, although he has no previous coaching experience.

The Mamic brothers decide on everything - and particularly on transfers, where Zdravko has a vested interest. He signed the so-called 'civilian contracts' with some of the players in their early development, binding them to share their future income with him.

Luka Modric, for example, is required to give up 20% of his wages to Mamic for as long as he's playing professionally. That means the Real Madrid midfielder is currently making him €900,000 per year, and the Jutarnji list daily newspaper claims he has similar contracts with 14 others. Mamic's son Mario worked as an agent for some of them.

Players who refuse to cooperate and sign long-term contracts often don't get to play and are marginalised. Andrej Kramaric was offloaded to Rijeka and is now the league's top scorer, and also a rising star in the national team. This summer, bright young prospects Robert Muric and Fran Brodic left for Ajax and Club Brugge respectively, after their youth contracts ran out.

Disapproving club members and journalists are treated as enemies, with Mamic insulting and threatening them in his press conferences, featuring long monologues akin to Fidel Castro.

Hardline supporters are regularly harassed by stadium security and police at Maksimir. Around 50,000 people have so far signed a petition demanding elections at the club. Club legends like Robert Prosinecki and the former Liverpool man Igor Biscan publicly supported the cause.

Expect showings of support for "free Dinamo" to surface at Celtic Park on Thursday. Rumours are the Bad Blue Boys, some of whom are in contact with Celtic fans, have prepared something and are hoping their hosts would be sympathetic to their struggle.