And McGowan admitted that the word among his fellow international players was that Postecoglou’s obsession extended to spending his nights playing the football management simulation computer game.
Speaking to 67 Hail Hail, McGowan, who now plays for Kuwait Premier League club Kuwait SC, said: "I would say he is beyond obsessed.
"Even at the World Cup, there was rumours going round that he was playing Football Manager in his room, because he was just in his room.
“I’m sure of it. He is just fully focused on everything, footballing-wise. Tactics, players, everything.
"He is obsessed with that, and it’s been a part of his life. That’s why he’s so successful, because of that obsession with it.
"He loves reading, he’s right up to date with everything that’s going on in the world, and he’ll be listening or taking advice from leaders.
"Leaders of tech companies, big businesses, of everything, picking apart all of those best bits that he thinks will make Celtic successful.
“He’s already shown that with winning a trophy in his first go, which took Steven Gerrard three years.”