His family had gathered at dawn outside an Iraqi army base in central Baghdad where he was expected to be released.
After waiting more than five hours, Dargham al-Zaidi said he received a phone call from Muntazer telling him he would not be released until the next day because of the delays.
The family said it will stage a sit-in outside the base on Tuesday until he is released, and called for other Iraqis to join them.
"According to his brother, the release of Muntazer is supposed to be delayed or postponed," Ali Al-Mashakheel, a Baghdad-based journalist, told Al Jazeera from outside the detention centre where al-Zaidi was supposed to be released.
"His brother did not say why - he doesn't know the reason - but his brother, quoting Muntazer's lawyer, said he already got the permission from the judge to release him today ... he was angry, threatening the government and saying 'my brother was supposed to be released'."
Although Bush, who successfully ducked to avoid the speeding footwear, laughed off the attack, the incident caused huge embarrassment, to both him and Nuri al-Maliki, the Iraqi prime minister.
The leaders had been speaking at a joint news conference in Baghdad on what was Bush's farewell visit to Iraq prior to being succeeded in office by then president-elect Barack Obama.
Al-Zaidi faces the prospect of a very different life from his previous existence as a journalist for Al-Baghdadia television, a small, privately owned Cairo-based station, which has continued to pay his salary in jail.
Al-Zaidi's boss has promised the previously little-known reporter a new home as a reward for loyalty and the publicity that his actions, broadcast live across the world, generated for the station.
But there is talk of job offers from bigger Arab networks, lavish gifts such as sports cars from businessmen, a celebrity status, and reports that Arab women from Baghdad to the Gaza Strip want his hand in marriage.