Khawaja, who turns 39 this month, had back spasms and failed to open in the first Test victory against England in Perth then was ruled out injured for the second in Brisbane.
He has since recovered but selectors opted to stick with Travis Head and Jake Weatherald at the top of the order, leaving the 85-Test veteran's international future in grave doubt.
Asked if there was a way back for Khawaja, who has been on a lean run of form, Cummins replied: "Yeah, potentially.
"I think the selectors have been quite adamant we're picking a side each week that doesn't necessarily mean it's got to be exactly the same team as the previous week.
"We do that with the bowlers, this week obviously Nathan Lyon's coming back in, he missed last week.
"One of Uzzie's (Khawaja) great strengths is he has scored runs at the top, he scored runs in the middle," he added.
"If we didn't think he'd be good enough to come straight in, then he wouldn't be here in the squad. So absolutely, I can see a path back at some point if needed."
As expected, Cummins returns after missing the first two Tests with a back injury and will lead the attack alongside the outstanding Mitchell Starc and Scott Boland.
Veteran spin king Lyon is also back after being axed in preference for an all-pace attack at the Gabba, with Brendan Doggett and Michael Neser making way.
Cummins said he was firing on all cylinders and raring to go.
"If I played in Brisbane, I would have probably been on limited overs, but this week it's just go and play like any other Test match," he said.
"It's been fantastic to watch," he added of the series. "I think it's lived up to the hype, captivating every session.
"I've loved it and itching to get out there. The boys have been fantastic, Steve (Smith) has led brilliantly and I feel like I'm coming into a pretty settled and happy side.
"Couldn't have gone any better from our point of view."
Australia third Test XI:
Jake Weatherald, Travis Head, Marnus Labuschagne, Steve Smith, Cameron Green, Josh Inglis, Alex Carey (wk), Pat Cummins (capt), Mitchell Starc, Nathan Lyon, Scott Boland