Australian soccer's hottest property, Mathew Leckie, is surprised.

He's surprised at his stunning World Cup displays, and surprised pundits now estimate his worth at about $10 million.

He's also surprised just how rapidly his stocks have risen, a month after signing a $1.09 million contract with German second division club FC Ingolstadt.

The attacking winger could now command a market price much higher but he doesn't regret signing the deal before the World Cup started.

"I didn't know what was going to come at this World Cup," Leckie said on Sunday.

"I always say that everything happens for a reason. So whether I could have maybe had other offers now after this World Cup if I hadn't signed, I never would have known."

Leckie's dash and dare has been, along with Tim Cahill's goals, the highlight of Australia's campaign which ends with their last group match against Spain in Curitiba on Tuesday.

The 23-year-old said his eye-catching performances, and those of Australia, caught him by surprise.

"The whole team as individuals have all surprised ourselves a little bit," he said.

"For me, I definitely didn't think we would compete this well with the teams we have played.

"There have been times, especially [in] the Holland game, we dominated areas of the game - to lose that game was very harsh.

"I think the whole world expected us to come here and just put 10 men behind the ball and hope to pinch results.

"Although we haven't got the results, the way we have gone about it and the way we have played is something very exciting for the country."

Leckie dismissed talk of Australia's match against defending champions Spain being a dead rubber, with both teams winless and to exit the tournament after the clash.

"[Coach] Ange [Postecoglou] pointed out to us that we have only won two games in the World Cups that we have been a part of," he said.

"So for us to get a win, but also win against Spain, a team that were World Cup winners four years [ago], that will be a massive achievement for the country."

Socceroos teammate, the emerging midfielder Ben Halloran, hopes injuries to two key colleagues gift him his greatest World Cup opportunity. Halloran is in the frame for a starting berth against Spain in the expected absence of Mark Milligan (hamstring) and Mark Bresciano (hip).

The 22-year-old Halloran has come off the bench in Australia's losses to Chile and the Netherlands, and admits being a substitute is a tough assignment.

"To be honest, both games, coming on, it has been quite difficult circumstances," Halloran said on Sunday.

"We have been losing and it's difficult to get the rhythm of the game in 20 minutes.

"But that is what you have to do when you're a substitute so you can't make any excuses."

Australia and Spain will end their World Cup campaigns after their fixture and Halloran said the Socceroos wanted to finish on a positive high note.

"We want to make a statement ... we want a result against Spain because we feel that our form doesn't warrant three losses," he said.

"If anything, it has probably made us focus more on the fact that we need to be professional and finish this campaign on a high.

"It's a World Cup match against the former champions.

"So if anyone is taking it lightly, they need to take a look at themselves." - AAP