The Socceroos have a third key player under a World Cup injury cloud, with the man who got them to Germany now fighting for full fitness.

Striker John Aloisi, whose penalty shootout strike sealed Australia's first World Cup finals berth in 32 years, will miss Thursday's friendly against Greece at the MCG.

Aloisi is battling plantar fascitis - severe inflammation of a band of tissue under the foot.

The 30-year-old South Australian achieved nationwide fame when he powered home the winning penalty against Uruguay in Sydney in November and whipped off his shirt on a victory sprint.

But he wasn't running anywhere near that speed as the Socceroos' training camp in Melbourne kicked off.

He was restricted to light training along with fellow injury concern Tim Cahill, and is resigned to not playing against Greece.

"It should be alright for the Holland trip which is important because I don't want to get any further injury before I go away," Aloisi said.

"I'm quite positive I won't be able to play on Thursday."

With striker Harry Kewell undergoing treatment in Europe for a groin strain and Aloisi and Cahill out of the Greece match, the untimely injuries have given coach Guus Hiddink several headaches.

Not the least of them is how to best work the trio back into the World Cup frame in the two friendly matches after Greece against Holland on June 4 and Liechtenstein on June 7, or whether to replace them in the 23-man squad should they fail to recover as hoped.

Injured players can be replaced up to 24 hours prior to the Socceroos' opening match of the tournament against Japan on June 12.

Aloisi revealed he thought his World Cup dream was over when he originally sustained the injury playing for his Spanish club side Alaves a fortnight ago.

"It was about 60 minutes into the game I came off and I was thinking it was all over, but the scans showed it wasn't a tear, which is good," he said.

"I know that it's not going to take too long to get back into it.

"Let's hope there's no setbacks, but at the moment, it's looking positive (for the World Cup)."

Cahill was also upbeat about his knee ligament injury, which has sidelined him for several weeks.

"I'm injured at the moment but things are looking really positive and we're working really hard," Cahill said.

"If we keep to the right procedures, things will be okay.

"I'm no chance of playing Thursday but I'm happy to be here with the lads and be a part of this camp."

The Socceroos trained twice on Monday, and in between sessions were feted by thousands of fans at a function at Federation Square in Melbourne's CBD.

Hiddink hinted at some experimentation against the European champion at the MCG on Thursday night.

Greece is likely to use its tried and tested lone striker formation with a five-man midfield against the Socceroos, with Euro 2004 final goalscorer Angelos Charisteas shouldering the load up front.

That could open the way for Hiddink to use a back-three and structure his midfield slightly differently to the way it was employed against Uruguay.

"Maybe we make some little changes, but not many," Hiddink said.

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