Mathew Leckie is a freak. A beast. A brother. A hero.

Teammates have long admired Leckie, who rivals Tim Cahill as Australia's best-performed player at a World Cup.

But the admiration has turned to outright awe after his match-winning goal against Denmark booked Australia a berth in the cup's knockout stages for just the second time.

"Such an animal. A beast," captain Mat Ryan said of Leckie.

"Getting up and down that touchline, doing a job for the team, so selfless.

"He is absolutely spent but he finds that energy in himself to make last-ditch challenges or go on that run that he went on and score that goal."

Leckie burst to prominence at the 2014 World Cup in Brazil and has since been the Socceroos' standout at the showpiece tournament.

"His football does him more privilege than any words I have got for him," Ryan said.

"He had obviously a great European career as well and it's for moments like tonight you can see why.

"He's a talented player and person and I am so glad to have him a part of this team."

Another teammate, Milos Degenek, described Leckie as "a freak".

"He has played in Germany for 10 years and you don't do that if you don't have the quality," Degenek said.

"I am very close to him and he is one player who deserves this more than everyone.

"I could only be happier if I scored. But he has done it and it's as if I have done it.

"I look at him like my older brother and I am very, very proud of him ... I love him to death."

Coach Graham Arnold was reluctant to individualise - but did so anyway.

"Mathew Leckie has been incredible," Arnold said of the Melbourne City linchpin.

"I can't just single him out because they all have.

"But you can see just watching Melbourne City ... you can see it in his eyes. He has got this hunger and drive.

"And he's such a wonderful guy."

The self-effacing Leckie tried to deflect attention from his heroics.

"With my celebration, you saw the emotion - I didn't really know what to do," he said.

"I was just pounding my chest and once the boys got together, the whole bench was there, and I think I got slapped in the head about 100 times.

"It just shows how much of a team we are.

"Whether boys are starting, coming off the bench or not getting any game time, everyone is here for each other.

"And it's so, so nice to be a part of this team."