Left-armer Starc was the third-highest Australia wicket-taker in the recent Test series in England despite playing just three games, claiming 11 scalps at an average of 32.45.
His absence would be a major blow for the hosts, who also have concerns over the fitness of fellow pacemen Ryan Harris, who injured his hamstring in the fifth Test at The Oval, James Pattinson and Pat Cummins.
There was better news, however, on Jackson Bird, who, if fit, is likely to come into contention for the first Test which starts in Brisbane on November 21.
Cricket Australia's chief medical officer, Dr Justin Paoloni, said in a press release: "Mitch Starc had scans following his arrival back to Australia and they have shown an early stage low back stress fracture.
"His management plan will be determined in the coming days but he is expected to be unavailable for a prolonged period."
On Bird, Dr Paoloni added: "Jackson returned home from the VB Tour of England with some lower back soreness.
"We have ruled out a major injury but will review scans in two weeks to confirm this. We expect that he will be available during The Ashes."
CA general manager team performance Pat Howard said: "While it's a disappointing result for Mitch, we know he will bounce back.
"Starc, James Pattinson and Pat Cummins are all under 24 years of age and we are certainly well aware that until fast bowlers get into their mid-20s they are more susceptible to injury.
"Historically, we've rarely seen three such promising young fast bowlers come through at the same time and all of a similar age so when they get injured of course that will be disappointing.
"We're doing our best to minimise longer-term injuries, but we are also realistic that such injuries are possible."