Massive blow for Australia with key batter out of third Test

Australia have suffered a massive blow just prior to the third Ashes Test against England with news that star batter Steve Smith will miss the match due to illness.

Smith had been battling illness in the lead-up to the Adelaide Oval contest and was ruled out on the morning of the match with veteran batter Usman Khawaja named as his replacement.

Australia skipper Pat Cummins confirmed Smith's absence from the team after he won the toss and elected to bat first on a bright, sunny day in Adelaide.

"He (Smith) is feeling unwell and he has headed off home," Cummins said.

"But we are lucky to have someone like Uzzie to come in."

Cummins said Khawaja will slot into Smith's preferred spot at No.4 in Australia's batting line-up meaning Travis Head will once again partner Jake Weatherald at the top of the hosts' order.

Cricket Australia later released a statement on Smith's wellbeing, confirming the right-hander is expected to recover in time for the Boxing Day Test in Melbourne.

"Over the past few days he (Smith) has been feeling unwell, with symptoms including nausea and dizziness," the statement read.

"He was assessed and monitored closely and was close to being available to play. However, given the persistence of symptoms, a decision was made not to proceed.

"He is being treated for a potential vestibular issue. This is something Steve has experienced intermittently in the past and is being managed accordingly. He is expected to be available for the Boxing Day Test in Melbourne."

It means the Aussies will enter the crucial Adelaide contest with three changes to the side that registered an emphatic eight-wicket victory in the second Test in Brisbane, with spinner Nathan Lyon joining Cummins and Khawaja back in the playing XI at the expense of Michael Neser, Brendan Doggett and Smith.

England skipper Ben Stokes suggested at the toss he would have also batted first in Adelaide, with the tourists making one change to their XI as Josh Tongue gets his chance and fellow seamer Gus Atkinson drops out.

Australia XI: Jake Weatherald, Travis Head, Marnus Labuschagne, Usman Khawaja, Cameron Green, Alex Carey, Josh Inglis, Pat Cummins (c), Mitchell Starc, Nathan Lyon, Scott Boland

England XI: Zak Crawley, Ben Duckett, Ollie Pope, Joe Root, Harry Brook, Ben Stokes (c), Jamie Smith (wk), Will Jacks, Brydon Carse, Jofra Archer, Josh Tongue

Ashes schedule

First Test: Perth Stadium, November 21-22 (Australia won by eight wickets)
Second Test: Gabba, December 4-7 (Australia won by eight wickets)
Third Test: Adelaide Oval, December 17-21
Fourth Test: MCG, December 26-30
Fifth Test: SCG, January 4-8