The Socceroos have received a big boost ahead of their World Cup round of 16 clash with Italy after their opponents' leading defender was ruled out of the match on Monday (TUE AEST) through injury.

Italian centre-back Alessandro Nesta - the linchpin of the team's much-vaunted defence - injured a groin during Italy's 2-0 win over the Czech Republic on Thursday.

Team doctor Enrico Castellacci told Agence France Presse Nesta would not play against the Socceroos, with Italian radio reports also confirming Nesta was out of the game.

It is expected Marco Materazzi, who scored Italy's first goal against the Czechs and was man-of-the-match after replacing Nesta off the bench, will retain his place at the heart of the Azzurri's defence.

Australia is likely to make at least one change, with Mark Schwarzer expected to return in goal to replace Zeljko Kalac, who had an unhappy game in the 2-2 draw with Croatia.

Socceroos coach Guus Hiddink has defended his decision to start Kalac ahead of regular goalkeeper Schwarzer against Croatia despite the move nearly tipping Australia out of the World Cup.

If not for Harry Kewell's 79th minute equaliser, the Socceroos would be on the plane home rather than facing Italy in Kaiserslautern after Kalac had conceded a horror second goal to gift Croatia the lead.

But Hiddink was unrepentant about using Kalac, despite a chorus of criticism for taking such a huge risk in a vital match.

"I don't regret this because both are good goalies and both have some problems in previous games," Hiddink said.

"Sometimes you can make some decisions, but it's very easy after a game to say that you not have done this.

"We'll see what coming up in the next game."

For Hiddink, the Italy match is a clear case of deja-vu after he guided minnow South Korea past the Azzurri at the same stage of the 2002 tournament with a golden goal winner in the round of 16 for a 2-1 win.

But he said it was important the Socceroos did not concede early goals, and take maximum advantage of the few chances they will get after several were squandered in the 2-0 loss to world champion Brazil earlier in the tournament.

"At that time it was maybe a different Italian team underestimating the Koreans, but I think it's different now. I don't think they underestimate anyone at this tournament," Hiddink said.

"Against Italy, you don't get many chances and I don't think we'll get as many chances as we did against Brazil."

The Socceroos cancelled training on Saturday, with the team expected to have one more session on Sunday ahead of the match in Kaiserslautern - about a 90 minute drive from their base in southern Germany.

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