Like the Socceroos, Denmark have been here many times before: a must-win game.

The Danes meet the Australians in the World Cup on Wednesday (0200 AEDT Thursday) with a simple equation: win, or depart Qatar.

The Socceroos have some wriggle room - a draw will be enough for Australia to advance from the group stage at a cup for just the second time.

Three of Australia's past four internationals have been in the do-or-die category.

First, they needed to beat the United Arab Emirates on June 7 to reach the interconintental playoff: they won, 2-1.

Second, the playoff against Peru six days later: they won on penalties.

Third, the World Cup encounter with Tunisia to stay in the hunt to get out of the group: they won, 1-0.

The Danes are also well-versed in such pressure.

At last year's European Championships, Denmark lost their first two games while reeling from the trauma of linchpin Christian Eriksen's on-field cardiac arrest in the first match against Finland.

At the Euros, all seemed lost but Denmark, using Eriksen's situation as inspiration, beat Russia 4-1 in their final group game and snuck out of the group on goal difference.

The Danes then made it all the way to the semi-finals.

"We definitely carry that with us," Danish forward Andreas Cornelius said.

"Many things happened in the Euros, the first game and all that.

"And then we came back and made it to the knockout games.

"It doesn't really matter how you get through, just as long we get through."

Eriksen is at the World Cup, his first major international tournament since that day in Copenhagen when his country and the football world watched in horror as he lay lifeless on the field.

Medics used a defibrillator to re-start his heart and save his life.

Cornelius was a substitute and sitting on the bench when Eriksen collapsed but said the experience had added to the resilience the team will need against the upbeat Socceroos.

Eriksen scored early against Australia in the final group game at the 2018 cup in Russia, only for then Socceroos skipper Mile Jedinak to convert a penalty in a 1-1 draw.

That result was enough for the Danes to reach the round of 16, where they were tipped out on penalties by Croatia.