IT’S confirmed.

Australia will not play with three centre-backs under Bert van Marwijk, with the Dutchman immediately working on a new defensive shape with the Socceroos ahead of friendlies against Norway and Colombia.

Ange Postecoglou’s shift to playing with three central defenders and two wingbacks polarised opinion after he pulled his selection bombshell against Iraq in Iran, and then continued with it all the way through until the play-off series with Honduras.

Van Marwijk has worked intensely on defensive shape so far in the two sessions in Oslo, and Mathew Leckie – who got through a lung-busting amount of work as the right wingback in the old system – has revealed that a 4-2-3-1 looks like the side’s new set-up.

“We trained the 4-2-3-1 yesterday in a defensive sense,” he told Fox Sports.

“We haven’t really spoken yet how we’ll go with the ball.

Leckie at training in Oslo. Source: Supplied

“It’s more about trying to manage it in a defensive sense – we’ve only trained two days. Today is more of a solid session and maybe we’ll get some more ideas today.”

ULTIMATE GUIDE: Key details for upcoming friendlies

DEFENCE: Who wins, who loses from Bert’s new plans?

Bert van Marwijk has some choices to make in Australia's defence. Source: FOX SPORTS

Many Socceroos observers pined to see Leckie, who had started the Bundesliga season in rampant form playing in advanced areas on the right for Hertha Berlin while Australia’s qualifying campaign reached its climax, also play further forward for his country without the defensive shackles on him.

When asked if the new formation meant an end to his wingback days, he said, with a grin: “Maybe, for now”.

The Socceroos warm up in freezing Oslo. Source: Supplied

“The training sessions are a little bit different, that’s normal,” he added.

“He’s pointed out we don’t have much time, but he’ll stick to the basics of telling us what he wants us to do, and try to make the most of the time we have.”

While van Marwijk impresses his new shape upon the side, the camp is also a golden opportunity for those on the fringes to impress the coach.

Tim Cahill, centre, warms up with his Socceroos colleagues. Source: Supplied

Training heats up in Oslo. Source: FOX SPORTS

One of those players he has handpicked to take a look at is Andrew Nabbout, and the Newcastle Jets sensation, who has just moved to Japan club Urawa Red Diamonds, revealed the fanatical details being impressed upon the side by their new boss.

“(He’s) strong on discipline and all round one-percenters, accuracy of passing, the movement is very good,” he told Fox Sports.

“His attention to detail is very, very good.

“It’s going to make us better players. The rest of the coaches are amazing, they’ve all got very, very good football knowledge and they know how to get the best out of players. You already see that in the first two days. It’s exciting and I can’t wait.

Van Marwijk ramped up the tactical preparations on Wednesday in Oslo and only allowed the media in for 15 minutes as he upped the ante in his preparation with the side.