Australia's Usman Khawaja set to start final Ashes Test but future remains uncertain

There had been speculation that the 39-year-old might announce his retirement following the Ashes but Australia head coach Andrew McDonald says no discussions have taken place about the batter's future.

"We've been really clear that we haven't had a conversation," McDonald said prior to training ahead of the Test that starts on 4 January.

"The speculation has been from the external. He's with his family at the moment, having a couple of days off.

"We'll build into Sydney, and we're always having conversations about where players are at and speaking directly with players. And there's no indication at my end that he's calling it in Sydney.

"So that'll be something that we'll discuss, but his performance in this calendar year has been good enough to warrant selection, so I'd say he'd be there marking centre in Sydney.

"Our challenge is if any of our great players retire is that you want to acknowledge them. But until that point in time when you're clear on someone's future, it's very difficult."

McDonald admitted Australia's batting unit was a concern after being bowled out for a set of low scores in the Boxing Day Test defeat.

The Australia mentor highlighted Marnus Labuschagne's regression in form through the Ashes was due to a lack of intent at the crease.

The number 3 made two fifties at a strike-rate of more than 73 in the opening two Test matches before absorbing 122 deliveries in Adelaide and Melbourne for just 46 runs at a rate of 37.

"I think with Marn, he won't mind me saying this, it's probably when he loses his intent to score he gets himself in bad positions," McDonald said.

"I think there's periods of time where he goes back into his shell and really trusts his defence.

"And I think within that creates a little bit of error in his game, and he's working on it."