The Rangers icon has been less than impressed with Tottenham in recent times, Postecoglou's current side.
The Australian took over at the Premier League giants during the summer of 2023, after winning the treble for the the Hoops.
It was his high-octane, high-pressing, all-out-attacking style of football in the Scottish Premiership that earned him the move to Spurs.
However, there have been more than a few occasions now where his approach to the game has not worked in England's top flight.
And Souness has branded it 'naïve ' as opposed to brave.
“When I think of Ange Postecoglou, I go back to that game against Chelsea where they got two players sent off and he still had them playing right up to the halfway line," the 71-year-old told Simon Jordan and Troy Deeney on William Hill's Three Up Front podcast.
"The only time you can do that is when you’ve got 11 players on the pitch and the ball is constantly under pressure.
“The minute someone can get their head up, you’re in trouble.
"They could have conceded four or five more goals that game – I thought that was naïve.
"It’s naïve to talk like that and say that the more open the game is, the better it is.
"If they’d lost that game seven or eight goals to two, you’ve lost the players as a manager. He wasn’t brave that day, they got lucky.
“He’s walked into Tottenham without bringing any of his own staff, is he so naïve as to think he can trust any of the coaching staff he’s inherited not to go to the chairman with their tittle-tattle?
"I would not take a job and think I can just walk into it – it’s madness – you need to go in with people you trust because being a manager is lonely."
On Spurs' most recent game, a 3-2 defeat at Brighton in which they collapsed to throw away a two goal lead, Souness questioned the team's leadership on the pitch.
He added: “The Tottenham players should have known better. You learn it at school – when you’re 2-0 up the next goal is vital.
"If you concede, the momentum is suddenly with the opposition but if you go to 3-0 up, the game is over.
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“I don’t know if Spurs have any leaders.
"When they go into the dressing room at half-time, the chat should be, ‘we can’t concede the next goal, this game is far from over’ – that’s what Ange Postecoglou should be telling them.
"He needed to remind them that if they were to concede, everyone’s going to be all over you.
“I think the issues at Spurs boil down to the manager and the coaching staff.
"The only message they needed to give the players in that game when the half-time whistle blew was to play more of the same.
"Spurs just ended up capitulating which is why Postecoglou was so deflated after the game, he thought he had some warriors in that team and was proven otherwise.”