Postecoglou said: "He's been great. For a younger player that's the hardest area of the pitch to come in and make an impression because you're usually only judged by one thing and that's your goal involvements, and everything else in your game doesn't really register.
"So especially for a young person like Brennan, who has come into a big club with a significant transfer, I think he's handled it well at every juncture.
"He's worked really hard in the areas we've asked him to work hard in and he's already got great qualities. That's why we brought him here. He's beginning to get the rewards now but that doesn't mean that stops.
"That's the beauty for him and all of the guys, that it's not about being satisfied with where you're at and if they keep having that attitude of wanting to improve, then that's going to make us a stronger team and them key contributors."