Australia won't take any risks with Michael Clarke's hamstring, with chairman of selectors John Inverarity rating the skipper only a 50-50 chance of being passed fit for the Boxing Day Test.
Clarke was forced to retire hurt in his second innings of the first Test against Sri Lanka in Hobart last week.
Inverarity and vice-captain Shane Watson both expect the world's No.1-ranked batsman to do everything possible to prove his fitness over the next couple of days.
But that might not be enough.
"He's a very precious asset and I would go low risk,'' said Inverarity after watching Sunday's MCG training session, where Clarke was limited to light duties.
"He's always upbeat, he desperately wants to play.
"But we certainly don't want to push him especially hard in a Test and for him to break down.''
If Clarke were to miss the second Test, his spot in the batting lineup would go to Usman Khawaja, with Watson assuming the captaincy.
The allrounder has never led Australia in a Test, although he did the job with some distinction in the limited-overs series in the West Indies earlier in the year.
"It's just about as big as it gets for an Australian cricketer,'' said Watson of the prospect of leading Australia in a Boxing Day Test.
''... It's an amazing opportunity to think that something like that has come along in your life.
"But I'm trying not to get too far in front of myself at the moment.
"I know Michael will be doing everything he can to get right for this Test match.''
Watson said he would trust his gut instinct if called on to captain an Australian side now also missing long-time skipper Ricky Ponting.
"Until you actually captain a side you don't really realise the intuition you've developed over those 10 or 11 years of playing first-class cricket and being around some of the best players who have ever played cricket for Australia,'' he said.
"Intuition really does come to the fore.''
The other pressing selection issue for Australia concerns the makeup of the pace attack - specifically whether Mitchell Starc will be rested despite claiming a match-winning, five-wicket haul in the first Test in Hobart.
Inverarity said the 22-year-old Starc would definitely miss one of the back-to-back Tests in Melbourne and Sydney as part of the rotational policy designed to avoid further injuries to Australia's depleted fast bowling stocks.
"It's about bowling loads,'' said Inverarity.
"The science behind it is that they've got to build up their bowling loads so the oscillations are not very significant.
"If they do become reasonably significant, as they have done for Mitchell, then you enter a danger period, a high-risk period.''
If Starc is rotated out of the Boxing Day Test, Tasmanian paceman Jackson Bird will be handed a first Test cap and Mitchell Johnson will return after being unluckily left out of the Hobart clash.