Socceroos goalkeeper Mark Schwarzer admits it is worrying that several of Australia's World Cup squad are under fitness clouds going into what they expect will be a gruelling pre-tournament training camp.

As fitness concerns swirl around several key players - most notably Harry Kewell - Schwarzer and midfield star Tim Cahill go into the tournament in perfect health and peak form.

It is arguable Schwarzer and Cahill are Australia's two most indispensable players in their bid to emerge from a difficult Group D in South Africa.

But with the Socceroos' top 12 or 13 players so set in stone, Schwarzer admits the prospect of any being underdone is a worry.

"It's always a concern when guys are injured heading into a big tournament," Schwarzer said ahead of the team's training camp which started in Melbourne on Wednesday.

"You want to have as many of your players fit as possible, especially your experienced players.

"But we've still got three weeks or so until the beginning of the World Cup, so it still gives players the opportunity to find their fitness, to overcome any niggles or injuries they've had over the season.

"Hopefully come the first game they'll all be fit."

Kewell's groin injury saga looks likely to be played out in daily episodes of "Harry-watch" leading up to Australia's World Cup opener against Germany in Durban on June 14 (Australian time).

He trained lightly with the team at their first training session at Melbourne's AAMI Park.

But he is likely to be eased through as the intensity rises with double sessions each day in the lead-up to the friendly against New Zealand at the MCG on Monday night.

There are no such concerns for Schwarzer, who at 37 has come off arguably a career-best two years.

He helped English Premier League club Fulham to the Europa League final last week, as well as being the Socceroos' best player throughout the 14-match World Cup qualification campaign.

Schwarzer and his teammates are expecting Pim Verbeek to employ the same sort of physically demanding training schedule previous coach Guus Hiddink used ahead of the 2006 tournament.

"It will be very intense - from last time I can tell you it will be a very intense situation," Schwarzer said.

"The first week is usually a bit lighter because of the many commitments we have here in Australia.

"But once we knuckle down, get away from the outside world a little bit, and get down to concentrate on training it becomes quite intense."

Cahill believes Australia's work ethic and experience from 2006 will be the keys to their performance in South Africa next month.

And he has also stressed the importance of Australia getting their first-choice players in peak condition to tackle the World Cup.

"First of all we have to keep players fit and then try to get the consistency," Cahill said.

"If we prepare right and try and be as fit as we can for this World Cup like we were for the last World Cup, our natural talents will hopefully shine through.

"We've got great character, great work ethic within the team and a team that sticks together."

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