National selector Mark Waugh has confirmed Australia will err on the side of caution regrading Mitchell Starc's fitness, with the spearhead an unlikely starter for the Boxing Day Test because of a foot injury.
Starc has been cleared of serious damage but remains in doubt for the fourth Magellan Ashes Test because of a bruised heel.
The left-armer, who remains on crutches because of the injury he suffered at the WACA, will land in Melbourne on Friday.
The painful injury requires rest and Starc has limited time to prove his fitness before Australia start their push for a 4-0 lead in the series at the MCG on Tuesday.
Selectors will be understandably keen to ensure Starc is fit for the four-Test Qantas Tour of South Africa that follows the Ashes.
"Common sense prevails," Waugh said on Fox Sports. "You ask the bowler how he's feeling (and) the medical staff will assess it as well.
"If it was 2-1 down or 2-1 up and this was a Test match we had to win, you might push the envelope a bit further than when you're 3-0 up.
"Common sense says, if he's not quite right I think they'll err on the side of caution. That would be common sense to me."
Australia are yet to declare Starc a non-starter, wanting to give the express paceman every chance to show his landing foot is up the rigours of five days of Test cricket.
If he is ruled out, Jackson Bird will take his place in Australia's XI.
Starc has played in just one Boxing Day Test since making his debut in 2011, and he's desperate not to miss it this summer.
"I'm sure whatever the case is, he's going to be doing everything he can to play on Boxing Day," Australia first drop Usman Khawaja said on Tuesday.
"He bowled beautifully this game. He was obviously in a bit of pain. But I think they're going to have to assess it in the next couple of days."
Former captain Allan Border also suggested it would be sensible for Starc to miss the fourth Test.
"He's had different problems with that same foot," Border told Fox Sports.
"Having secured the Ashes, probably no real need to risk Mitchell in Melbourne. Hopefully he gets himself right for the Sydney Test."
Starc noted on Wednesday that "if it's up to me, I'm playing".
"But I think there's a few other people in that conversation," he told the Nine Network.
"It's not up to me. I'll get there on Friday and see how it pulls up over the next few days."
While it had been 39 years since England had won an Ashes Test at the WACA Ground, the tourists have a significantly better record in Melbourne.
In their last 10 Tests at the MCG stretching back to 1979-80, England have won four and lost six, including an Ashes-sealing win – by an innings and 157 runs – in 2010.
England are now playing for pride after losing the first three Tests of the summer by margins of 10 wickets, 120 runs and an innings and 41 runs.
2017-18 International Fixtures
Magellan Ashes Series
Australia Test squad: Steve Smith (c), David Warner (vc), Cameron Bancroft, Usman Khawaja, Peter Handscomb, Shaun Marsh, Mitchell Marsh, Tim Paine (wk), Mitchell Starc, Pat Cummins, Nathan Lyon, Josh Hazlewood, Jackson Bird.
England Test squad: Joe Root (c), James Anderson (vc), Moeen Ali, Jonny Bairstow, Jake Ball, Gary Ballance, Stuart Broad, Alastair Cook, Mason Crane, Tom Curran, Ben Foakes, Dawid Malan, Craig Overton, Ben Stokes, Mark Stoneman, James Vince, Chris Woakes.
First Test Australia won by 10 wickets. Scorecard
Second Test Australia won by 120 runs (Day-Night). Scorecard
Third Test Australia won by an innings and 41 runs. Scorecard
Fourth Test MCG, December 26-30. Tickets
Fifth Test SCG, January 4-8 (Pink Test). Tickets
Gillette ODI Series v England
First ODI MCG, January 14. Tickets
Second ODI Gabba, January 19. Tickets
Third ODI SCG, January 21. Tickets
Fourth ODI Adelaide Oval, January 26. Tickets
Fifth ODI Perth Stadium, January 28. Tickets
Prime Minister's XI
PM's XI v England Manuka Oval, February 2. Tickets
Gillette T20 trans-Tasman Tri-Series
First T20I Australia v NZ, SCG, February 3. Tickets
Second T20I – Australia v England, Blundstone Arena, February 7. Tickets
Third T20I – Australia v England, MCG, February 10. Tickets
Fourth T20I – NZ v England, Wellington, February 14
Fifth T20I – NZ v Australia, Eden Park, February 16
Sixth T20I – NZ v England, Seddon Park, February 18
Final – TBC, Eden Park, February 21