The Olyroos need to win their final group match of the AFC U23 Championship, against South Korea on Wednesday night, to give themselves the best possible chance of reaching the knock-out stage.

It comes after Australia dominated with a whopping 75 per cent of possession but were unable to break down a five-man Vietnamese defence on Sunday night, before slumping to a 1-0 defeat.

Milicic admitted it was a disappointing result but not as surprising as some back home might think, considering the investments made by other nations in youth football - and the fact Australia has not matched them.

"I don't know where we get the expectation of easy games and just thinking that we're going to win these games at youth level," Milicic told AAP from China.

"(The Vietnam team has) been together for a long time and a few years back, that same group played against Australia and won 5-1.

"I wouldn't go as far as to say our system's broken - far from it.

"However, a lot of other nations just put in a lot more into their youth programs and it's moving at a quicker rate than our development."

Milicic is adamant the answer lies in more minutes for young Australian players - at both club and international level - and more experience against different styles of opposition.

"Coming here to Asia, they're going to encounter experiences that they're not used to and many of them have not come across a team that sets up as a 5-4-1," he said.

"If we're going to have a serious program, we definitely have to use the FIFA windows more frequently because with the rate we're going, the exposure for these young boys isn't enough."

Australia will face an entirely different challenge against South Korea, who are a direct, physical team full of K-League regulars.

The Olyroos will be without winger Bruce Kamau (hamstring) and Milislav Popovic (ankle) and need to avoid defeat as well as hope for a favourable result in the other Group D fixture, which will be played simultaneously, to qualify for the next round.

Australia's results at the tournament will affect the team's seeding for the next AFC U23 Championship in two years, which doubles as the qualifiers for the 2020 Olympics in Tokyo.