Cummins rated Starc a "50-50" chance of overcoming a bruised heel to play in Melbourne, but selectors have already indicated they will take no risks with the Ashes series already won.
Cummins, who suffered a similar foot injury following his Test debut in 2011 and was out of action for more than four months, said Starc was keen to play in what would be only the second time in the showpiece Melbourne Cricket Ground Test.
"The injury is not super common, but if it's not treated well it can drag on for a very long time," Cummins told reporters on Saturday.
"It's a bruise pretty much where you've got to walk all day and bowl.
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"I'm sure they'll (selectors) come to an agreement and if he knows he's not right, he'll put his hand up.
"I chatted to him about it. I had a similar one and it's one of those where there's no way around it. You can't strap it differently, you can't bowl off the other foot or anything. It's hard to hide.
"He knows that, the staff know that and I'm sure they'll work it out."
Starc, wearing a compression sock on his right ankle, did not take part in Australia's training on Saturday.
He spoke with coach Darren Lehmann and selector Greg Chappell at the ground and also conferred with the team doctor and physio.
If Starc is ruled out, Jackson Bird is expected to play his first Test since last year's Boxing Day Test against Pakistan.
"I'd say that's certainly the thinking of a lot of people: the selectors, the skipper and everyone around him," Cummins said.
"He's doing everything he can to get right. He's been on crutches the past few days to try and take some weight off his heel.
"He hasn't tried to bowl yet ... I think in the next couple of days we'll assess that."
Bird has been part of the Test squad this year but couldn't break into the team when Starc broke down during a tour of India and when Josh Hazlewood suffered a side strain during a series in Bangladesh.
"I've been ready to go for 12 months basically."
Wicketkeeper Tim Paine is yet to join the squad after his father-in-law suffered a stroke but he is expected to be behind the stumps for the Boxing Day Test.
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