Van Marwijk's side lost to France in their opening game, putting up a brave fight before ultimately falling to a 2-1 defeat that left them needing to avoid a second defeat if they are to maintain realistic hopes of staying in the tournament.
The Dutch coach, who was appointed in January only months after guiding Saudi Arabia through qualification for Russia, said Australia should expect to face a physical challenge when they take on the Danes.
And while they will not face the same calibre of individual talent as they did against France, Denmark will be a more of a unit, according to van Marwijk.
"The Danish they are a strong team, they are number 12 in the world rankings and that says enough," Van Marwijk said.
"They are a physically strong team, very tall players, that's their weapon and we played against France and they have more quality and creativity in their players, but I think the Danish are maybe more a team."
If Australia are to beat Denmark, they will have to find a way of breaching a defence that has kept five successive clean sheets and last conceded a goal 534 minutes ago.
There have been calls from Australian fans and pundits for van Marwijk to introduce 38-year-old record goalscorer Tim Cahill, who was left on the bench for their defeat to France.
Daniel Arzani, the youngest player at the World Cup at 19, is also pushing to be included in the starting line-up after making a late cameo appearance off the bench in Australia's opener.
Van Marwijk, however, was giving little away in a guarded news conference where he often gave brief responses to questions.
"I will not talk about changes or not changes, we analysed the game very well," he said.
"Denmark will be a very difficult team to play against, but we get more confident every day in the way we want to play and I think that is very important.
"Now we only have to look at the details, first we have to do exactly the same as we did in France, with all the discipline, and now we have to find in detail things where the Danish can have problems."