Australia face a must-win qualifier against Saudi Arabia in Adelaide on Thursday if they are to keep alive their direct qualification hopes for next year's World Cup finals.

The Socceroos, who have qualified for last three editions, trail the Saudis and group leaders Japan by three points with three games left in Asia Group B.

The top two teams will progress to Russia 2018 with the third-placed nation forced into play-offs.

Both Australia and Saudi Arabia also have to play Japan in the remaining matches, adding a further edge.

It has been a muddling campaign for Ange Postecoglou's Australians, who are the only unbeaten team in the group but have had four draws among their seven games.

"Saudi Arabia are in a good position on the table and we need to not just draw but win -- it's a must-win," German-based attacker Mathew Leckie said.

But he added that the team was "very confident" and "very strong at home".

"We will definitely cause a lot of problems for them and if we play at our best, it will be tough to stop us."

The Australians were on track for all three points in their away match in Jeddah last October before a 79th-minute equaliser from Nassir Al-Shamrani in a 2-2 draw.

Scoring has been an issue for the Socceroos and QPR midfielder Massimo Luongo believed an early goal would be vital to unlock the Saudi game plan of containment in Australia.

"A goal early would ruin their game plan and they'll be forced to come out and try and score, and that will help us," Luongo said.

"A draw might be good enough (for the Saudis) but if we get a goal it's just going to unlock them. They they'll need to come out and play."

Dutchman Bert Van Marwijk's Saudi squad has been together for most of the last month.

The team was in Frankfurt for two weeks, followed by a week in Saudi Arabia before their early arrival into Adelaide to prepare for the qualifier.

Saudi Arabia have not made an appearance at a World Cup since Germany in 2006.

Source: AFP