Injured Australia captain Pat Cummins bowled for the first time since July on Wednesday as he races the clock to be fit for the second Ashes Test against England.

The 32-year-old pace spearhead has not played since picking up a lower back injury against the West Indies more than three months ago.

But he made a tentative return in a brief net session in Sydney captured by local television cameras, bowling off a five-step run-up.

Cummins has been ruled out of the first Test against Ben Stokes' England in Perth from November 21, with hopes that he will be ready for the second day-night contest in Brisbane on December 4.

"We're on the journey to that second Test and very hopeful that that will be a positive outcome," Australia coach Andrew McDonald said on Monday of Cummins.

"We will see how he pulls up and then we'll make decisions moving forward."

Steve Smith will captain the side in Cummins' absence with Scott Boland almost certainly replacing him to join fellow quicks Mitchell Starc and Josh Hazlewood.

Australia are still grappling with who will open the batting alongside Usman Khawaja.

Incumbent Sam Konstas' form has nosedived and he was again out cheaply in the Sheffield Shield on Thursday, bowled for 10.

Selectors are due to finalise their Ashes squad at the end of the current round of the domestic red-ball competition with Matt Renshaw and Marnus Labuschagne also in the running to be opener.