England wicketkeeper Matt Prior played down fears over Alastair Cook’s fitness today after the skipper missed his side’s first Ashes warm-up.

Prior, standing in for Cook as captain, insisted: “Him missing this game is purely precautionary, so I’d be very surprised if he doesn’t play the next one.”

Seamer Stuart Broad is also sitting out the three-day match against a Western Australia XI which started in the small hours of this morning.

Both have sore backs but Prior is taking the positives from what he sees as a chance for fringe players to impress.

Michael Carberry will probably replace Cook at the top of the order while all three of England’s tall fast bowlers are likely to feature at a venue known for its bouncy pitches.

Steven Finn, Chris Tremlett and the uncapped Boyd Rankin will be competing for the fourth place in England’s Test attack alongside first-choice picks Broad, James Anderson and Graeme Swann.

Prior said: “Nets have been good fun at the moment with the big guys steaming in, all playing for their place — the batters have been hopping around a little bit.

“It’s great to have competition in a team and in a squad.

“It’s not just in the bowlers — it’s batters, all-rounders, throughout the team.

“Everybody’s pushing each other very hard.”

Cook is expected to return against a strong Australia A in Hobart on November 6.

His absence there would give England a real headache, with only one more warm-up — against a New South Wales XI a week later — before the first Test on November 21.

England’s batting looked brittle in the home Ashes win and the squad includes several inexperienced batsmen.

County veteran Carberry has played one Test, against Bangladesh in 2010, while Gary Ballance and all-rounder Ben Stokes are uncapped.

But alongside them are 10 men who played in the 2010-11 win Down Under.

Prior said: “We’ve got a lot of our squad who know about playing cricket in Australia, and winning in Australia — which is a huge thing and a great confidence boost.

“Immediately we go into our first net session and batters with experience of batting on wickets with more bounce are feeding back to the younger players.

“Areas you need to change, types of deliveries you need to bowl on Australian wickets — all this information is immediately being filtered down.”

Cook’s opposite number Michael Clarke had a much better day today as he returned ahead of schedule from his own back injury and hit 88 for New South Wales against Tasmania.

He admitted there was a “bit of rust” but said he “felt completely fine” afterwards.