Former BMX world champion Sam Willoughby is making great strides in his recovery from a horrific spinal injury, his father says.

Colin Willoughby says his son's rehabilitation following the injury, suffered during a training ride in September, is going well.

The two-time Olympian, who was raised in South Australia, returned to his home in San Diego at the start of the year for the recovery process after spending months in hospital in Colorado.

"He is doing physio four times per week and can now hold himself up on a stationary bike and, with support, can actually pedal as well, which is great," Willoughby's father said.

"Sam is working hard every day in his recovery and knowing he has so much support back here in Australia really keeps him going."

The SA government will auction off a hot lap with racing driver Lee Holdsworth, who is in Adelaide for the Clipsal 500 event, to raise money to aid Willoughby's recovery.