A Zagreb county court judge rejected a prosecutors demand that Mamic, detained for questioning on Friday, remain in one-month custody and he was immediately released.
Mamic, considered the most powerful man in Croatian football, is suspected of 'publicly inciting violence and hatred ... against both the minister and all ethnic Serbs', a prosecutor's statement read.
If eventually charged and found guilty Mamic could be sentenced up to three years in jail.
Mamic told a local radio station on Friday that Education Minister Zeljko Jovanovic, an ethnic Serb, 'hates everything Croatian' and was an 'insult to the Croatian brain'.
"When he looks at you, blood squirts from his eyes ... Looking at his smile, one can only see eye-teeth ready for slaughter," Mamic told Soundset radio.
The comments could not have come at a worse time and risk stoking tensions ahead of a 2014 FIFA World Cup qualifying match between the two former foes next week in Zagreb.
Serbs make up Croatia's largest minority, accounting for around four per cent of the country's population of 4.2 million.
Relations between Zagreb and its ethnic Serbs remain sensitive since the 1991-1995 war during which Serb rebels fought against the former Yugoslav republic's independence.
Mamic's statements were immediately strongly condemned by the country's top officials, the Serb community and the rights groups.
The Croatian Football Federation (HNS) said the statements by a member of its executive committee were 'unacceptable' and announced a disciplinary procedure against Mamic.
Respect for minorities' rights was a key condition set by the European Union for allowing Croatia to join the 27-member bloc. Croatia will join the EU on 1 July.