Postecoglou has had a nightmare start of Forest, who are winless in his seven matches in charge across all competitions. After such a poor campaign so far, many have called for him to be sacked, which has frustrated Rooney.
Speaking to the BBC, Rooney was shocked to hear such rumours of Postecoglou potentially losing his job after so few games in charge.
“It’s crazy. All the rumours that you heard about him, that he could get sacked after six or seven games, it’s absolutely crazy. And I like him, I think he’s a good man," he said.
"He obviously struggled in the league with Tottenham last season, but then he went and won the Europa League. It was strange seeing Nuno (Espirito Santo) get sacked at Forest, and then they brought Ange in. If he does get sacked, I think it’s absolutely wrong."
The shortest managerial reign in Premier League history is held by Sam Allardyce, who was in charge of Leeds United for 30 days. Postecoglou has just a few days to survive to beat that record as he looks for results to improve.
Rooney added that he hopes Postecoglou gets more time, especially after lifting the Europa League with Tottenham last season when he proved he still has what it takes to create a successful side.
“It’s tough, but Ange Postecoglou is a good man. He’s won trophies everywhere he’s been, and I hope he gets the time. But from everything you hear, the Forest fans don’t look like they’re willing to give him that time.”