Former Socceroos star Jason Culina believes Australia coach Ange Postecoglou will need to settle on a preferred squad sooner or later ahead of the 2018 FIFA World Cup in Russia.

Postecoglou could cap as many as three new players in the upcoming World Cup qualifiers against Tajikistan and Jordan as he continues to build the depth of his squad.

Apostolos Giannou headlines a host of new talent, after the striker had played in a friendly for Greece before pledging allegiance to Australia.

He is joined in the squad by newcomers Jason Geria and Alex Gersbach, and while Culina acknowledged the importance of having a number of options, he feels stability is also important.

"There's no doubt it's important to build depth within your team and he has most definitely given many players an opportunity," the former PSV midfielder said.

"In saying that, he is still searching for his best possible squad and that [may be] a squad of 15 or 16 which he has in mind, and then another eight to 10 players on the fringe."

Culina said, thus far, Postecoglou's results had vindicated that approach.

The Socceroos won the Asian Cup in 2015 and remain on course in their qualifying campaign for Russia 2018, but Culina would still like to see a more solidified squad.

"Overall, I think it's still a side in transition," he said. "Ange has not decided on a final squad, but nor have some players given him a reason to keep them in there.

"But he can't keep turning over this many players and he has to settle on a squad and give them a really good opportunity."

While Culina believes the current level of rotation is unsustainable if the Socceroos are to go beyond their best ever result at a World Cup, he believes the players have to be accountable and challenge themselves at a higher level.

"Our players these days are in a comfort zone [in the A-League] and if you don't push yourself out of that comfort zone and look for a new challenge, you won't improve," Culina said.

"Players don't realise how much more they have within themselves unless they are really pushed.

"Our players need to realise that if they want to push themselves and improve, they have to play at a higher level. It's not just a physical commitment, it's a mental commitment to say, 'I want more from myself, for my life and for my game.'

"I told many players when I came back to [the now-defunct] Gold Coast [United] and Sydney FC that there is opportunities for themselves to play at the highest level … but it comes down to the mentality and whether they are desperate or willing enough to play at that level.

"My generation did everything we possibly could to play in Europe and that should be the goal of every player."