Champion cyclist and rower Amber Halliday remains in a critical but stable condition after suffering head trauma in an accident.

Halliday, 31, was competing in a women's bike race at Victoria Park in her native Adelaide on Monday afternoon when she crashed.

The three-time rowing world champion and last year's Australian cycling time trial champion is under sedation in the intensive care unit of the Royal Adelaide Hospital.

A post on Halliday's Facebook page read: "Amber has suffered serious head trauma from the crash.

"Her condition (is) classed as critical but stable.

"She has been sedated since the crash and has had various tests.

"She is suffering from bleeding and bruising of the brain among some other injuries including facial fractures.

"Due to the nature of head traumas, we face a delicate wait to hear of more information."

It is understood Halliday was the only rider who crashed in the incident.

"All of us are hoping she makes a quick recovery," said fellow cyclist Chloe Hosking, who competed in the same race.

"You don't want to see anyone crash and hurt themselves like Amber has."

Halliday switched from rowing to cycling after the Beijing Olympics and also quickly had success in her new sport.

But she underwent shoulder surgery late last year and could only manage seventh earlier this month when defending her Australian time trial championship.

Halliday has also worked as a newspaper sports journalist in Adelaide.

Roger Vaughan, AAP

The AOC wishes Amber Halliday and her family well for a safe and speedy recovery.