Most of Australia is, but Argentina coach Lionel Scaloni insists he's not shocked to meet the Socceroos in a World Cup knockout game.

"I wasn't surprised, honestly, because they are a good national team," Scaloni told reporters.

"We don't need to be overly confident ... it will be a tricky game."

Scaloni's side, ranked world No.3, enter their round-of-16 encounter on Saturday night (0600 AEDT Sunday) in Doha as the hottest of favourites.

But he downplayed the pressure of expectation against the 38th-ranked Australians.

"Whether they are inferior or not ... I don't fully agree," he said.

"They are a good team and this is football, it is 11 vs 11, this is the reality.

"So we need to leave aside the favourites and we need to play the game."

Scaloni highlighted Australian winger Mathew Leckie as among the chief threats but said he was most impressed by the Socceroos as a collective.

"They are playing in high levels and, especially, they are a team," he said.

"And when you are facing a team it is always difficult - and by team I mean a national team with players who know what they want.

"They have very fast wingers and their main strength is their counter-attack so we need to be very careful.

"We will break our backs on this pitch to compete but we know how difficult this World Cup is, this is football.

"When you say big national teams deserve to be in the next stage, that doesn't always happen."

Doubts remain over the fitness of Argentina's influential winger Angel di Maria, with the veteran substituted in their last game with an undisclosed injury.

"We hope he will be fine and will be able to play but I can't tell you at the moment because we don't have a clear picture," Scaloni said.