Kangaroos coach Tim Sheens admits injuries to key players are part of the reason for Trent Barrett's call-up, but is staying coy on the players he is concerned could miss the Four Nations series.

Cronulla captain Barrett was named as a late reinforcement in Australia's train-on squad on Tuesday amidst speculation Test skipper Darren Lockyer could be in doubt.

Lockyer quelled those concerns as the squad gathered for a training session at the Sydney Football Stadium on Wednesday, while veteran prop Petero Civoniceva also said his foot injury was on track for him to make the flight to England on October 17.

Lockyer, Civoniceva and Ben Hannant (shoulder) all completed Wednesday's training, which several Prime Minister's XIII representatives, including Johnathan Thurston, skipped in favour of a pool session.

Sheens did admit Manly fullback Brett Stewart (knee) would "struggle" and seemed to suggest there were also doubts over Penrith's Luke Lewis and Newcastle's Kurt Gidley ahead of the naming of the official squad on Tuesday.

"We've got quite a bit of injury to consider too, just quietly, there's more than most people would be aware of so we've got a lot of work to do before we finalise the squad," Sheens told reporters.

"A lot of them have still got another week to get ready so we'll wait and see what happens before we start naming people, but suffice to say there is more injury than I would like."

Sheens said the late inclusion of 31-year-old Barrett, who last played for Australia in 2005, was partly due to concerns over Lewis and Gidley.

"Based on the injury issues that we have amongst some of the key players, particularly my utility players in Kurt (Gidley) and Luke Lewis, the sort of players that have got a bit of utility value, I think Trent brings a bit of that, plus his experience in England," Sheens said.

"The selectors thought maybe we'd add him at this stage. That's no certainty but at this stage bringing him in, he covers Locky (Lockyer) as well so there's a bit of thinking about that."

Lockyer, though, declared he was in no doubt for the tournament, which kicks off on October 23.

"I'm feeling fine, why Barrett's been brought in I'm not sure," Lockyer said.

"At the moment I'm physically fine."

Civoniceva also said his injury was progressing well.

"The medical staff are really happy with the way it's responding and I've been up and running now for the last couple of weeks so I've been pretty happy with it," he said.

"It looks really positive for going away so all I have to do is keep up with the rehab work and the fitness training and hopefully I'll be a chance."

Barrett has fully recovered from a fractured cheekbone and eye socket which forced him to miss the Sharks' final six games of the NRL season.

Having spent two years at English Super League side Wigan, he said the England side Australia face will have a new look.

"They'll be a bit of an unknown this year, they've got some young players who I think they'll pick," Barrett said.

" ... There's a bit of a changing of the guard there, the (Kieron) Cunninghams, (Sean) Longs and (Paul) Sculthorpes have gone."

Australia's first match is on October 24 against World Cup holders New Zealand in London.

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