The forward has quickly become one of the most important players at the club this season.
Kulusevski has been working hard on and off the ball, crediting his immense stamina as being crucial to his success.
Asked about that, Postecoglou told reporters: “It’s not a fluke. It’s a lot of hard work. There’s some science there, some genetics or DNA. He just has a real capacity to be able to run at a certain level consistently. His recovery rates are really elite in that he can go and rest quickly and go again.
“But there’s also that mental strength to do it. A lot of players have the capacity but maybe reach the limit where they naturally get tired and don’t go again until they need to. But Deki will keep going and going. It’s a big part of his football, it’s a big strength of his.
“Again I’m not a biomechanist but his running efficiency is really good. He doesn’t seem to use too much energy. Or that’s how it looks to me. That could be a load of crap, I don’t know. But he does. If you think about it. If you’re trying to stop him and in he’s in your vicinity, you think he’ll go once, twice, or three or four times and that can wear oppositions down. He has the quality as well.
“We have to be mindful of not overburdening him because he’s played a lot. And with the squad we’ve got he’s played in the middle and on the wing. We don’t want to diminish that but at the moment he still feels really good. And it’s a big part of his game.”
Asked if Kulusevski is improving his game similar to how Cristiano Ronaldo and Harry Kane did earlier in their careers, Postecoglou added: “Yeah absolutely, spot on. He's very ambitious about how good he can be and that's a great thing.
“He's still relatively young and for his position, there's a lot of improvement in him. I've just got a feeling with Deki that he's not going to settle for any level apart from being the absolute best and it's great for us.”