Luke Plapp is out of the Tour Down Under with the Australian cycling star failing to recover from the injuries sustained in his crash the day before. 

The three-time reigning Australian road champion suffered severe road rash, from the back of his left shoulder down to the hip, when he crashed near the end of stage three.

Plapp had wanted to stay in the race, but his Jayco AlUla team announced on Friday morning he would not start the 136.2km stage from Murray Bridge to Port Elliot.

"After monitoring Plapp overnight, unfortunately he will not start today's fourth stage of the Tour Down Under due to discomfort and ongoing pain from a large amount of wounds," the team announced.

French rider Rudy Molard, who was also caught up in the crash, posted a photo from hospital showing the extent of his injuries, with significant road rash across his face, shoulder, and knuckles.

It was a painful reversal of fortunes for Plapp, who started the year by winning his third-straight national road race title.

He also regained the time trial championship at the nationals.

At Monday's pre-race media conference for the Tour, Plapp said the team was aiming for a sweep of the stages and the overall title — something no-one has done in race history.

But after Jayco AlUla dominated the nationals, winning five of the six elite races, the team did not win a stage in the women's race and so far has not won any men's stage either.

Plapp's injury means the team's Australian sprint ace Caleb Ewan loses a valuable lead-out rider for Friday — the last sprint stage of the Tour.

Ewan was ill in the days before the Tour and has lacked his usual spark in the sprint finishes over the first three days.

The race ends on the weekend with summit finishes for the last two stages at Willunga and Mount Lofty.

AAP