A path remains for Arnold, the reigning A-League championship winner, to assume control of the national team.

The 54-year-old spent a decade involved with the Socceroos, acting as an assistant coach to Frank Farina, Guus Hiddink and Pim Verbeek.

He was also briefly head coach in 2007, leading Australia to an underwhelming quarter-final finish at the Asian Cup after Hiddink's departure.

Arnold has since risen to become the A-League's pre-eminent coach, demonstrated by the Sky Blues' record points haul and double-winning 2016-17 campaign.

It means he is in the frame to return to the role a decade on, as a more experienced and wiser candidate, but it will only transpire should certain events come to pass.

Firstly, the Socceroos would have to qualify for the World Cup.

Arnold wouldn't consider leaving Sydney FC midway through a campaign, and if Australia fails to reach the 2018 tournament, FFA are likely to consider a foreign, ship-steadying, boss.

Secondly - and most obviously - FFA must want him.

Arnold is well thought of by head office, with his efforts in 2007 considered ancient history.

Thirdly, he needs to repeat his club success this season.

Should the Sky Blues become the first club to defend their A-League premiership, Arnold's candidacy for the Socceroos job will be impeccable.

Finally, Sydney FC would have to allow it.

Arnold is contracted until the 2018-19 season and wouldn't walk away without their blessing.

Should those circumstances arise, Arnold says he would be a candidate.

"I'm not saying I wouldn't want the national team job; if my country calls, of course I would," he said.

Postecoglou has made clear he won't stay after this World Cup cycle.

That means leaving the job either after next year's tournament or sooner, should the Socceroos fail to beat Syria or their North/Central American opponents in play-offs this month and next.

Missing the World Cup remains a concerning possibility, but Arnold has been a vociferous supporter of Postecoglou's tenure.

Arnold backed Postecoglou to reach Russia and to set up his successor for future success.

"People were calling for rejuvenation of the squad when Ange took over," he said.

"He did it and he's continued to do it. In four years the squad will be fantastic.

"Look at the golden generation - which I called it that for the first time in 2006 - they were all 28, 29, 30 at the World Cup in 2006.

"We now have players that are 23, 24 and they're coming through. They're probably, at this moment, not in their peak years.

"Harry Kewell, John Aloisi, Mark Bresciano and others ... when we played Uruguay in 2001 they didn't have the experience.

"When we got to 2006 they did and could handle any occasion.

"These guys now, they are the future generation. I know they will qualify.

"These extra few games are going to bring the team together all the better."