The shot stopper is out for most of the season with a serious ankle injury, which has been revealed as a fracture.
Postecoglou praised the toughness of Vicario and admitted that he would be a miss.
He stated: “I guess, a bit of a shock first of all. We saw he picked up an injury during the game. We saw at half-time but there was no doubt about him continuing. You kind of digest that. Post game he was sore but he played 60 minutes with a sore ankle. We will tape it up and go again.
“But, and I guess externally now people realise, it is a testament to him as a person. He is as tough as nails, as tough as they come. The fact he played at that level for 60 minutes with a fractured ankle was quite outstanding.
“When the shock off it wears off, you process he is going to be missing for a while. Knowing him, he will push the limits as to how long that is and you will get daily updates about that through his Instagram.
“Big blow, but for him personally I guess because he was having an outstanding season for us and really growing as a leader within the group. But we have dealt with setbacks before and we will deal with this.
Postecoglou added on Vicario being a hero for playing through the pain in their last game: “Yeah I think so. Externally people probably now realise what we knew about him internally.
“It is the reason why I made him part of the leadership group this year because you just see the way he goes about his business on a daily basis. He has a really strong mentality. He wants to be better. I give the guys days off, I guarantee he will be in anyway doing something He is just that kind of person.
“An unbelievable performance. Irrespective of the injury it was a really strong performance from him but taking that into context it is certainly one for the record books of this club in terms of outstanding performances”
On the recovery timeline, he finished: “Not really. It’s not going to be weeks, it’ll be months. He’s had surgery and there’s certain timelines.
“Because it is Vic, and I don’t like giving timelines so early in a process like that because it puts undue pressure on the players and some expectations, but once we get past the rehab stage and he’s getting out there we’ll have a clearer idea.”