A koala has been released back into the wild after miraculously surviving a 16 kilometre trip clinging onto the underside of a car wheel arch.

Jane Brister, a Koala Rescue Specialist at Fauna Rescue SA, was called to a suburb in Adelaide last week after a driver reported hearing "unusual sounds" and "crying" coming from his car.

Kelly the koala was trapped behind a tyre as the truck made a 15km trip through Adelaide Hills.

The driver had driven from his home in the Adelaide Hills district to the city, a trip he estimated to be nearly 16 kilometres, according to Brister.

"Early in his journey, an oncoming driver flashed his lights at him, and so he thought there must be something wrong with his car," Brister said. "But [when] he pulled over... he couldn't find anything in the dark."