Reigning champion Toby Price is out of the Dakar Rally after suffering a broken leg in a motorcycle crash.

The Australian Red Bull racer fell off his motorcycle during the fourth stage and was airlifted to hospital before being diagnosed with a fractured left thigh bone.

The 29-year-old, who became the first Australian to win the two-week race in any category last year, headed into Thursday’s (Friday AEDT) stage in fifth place overall.

Price was reportedly leading the 416km stage between San Salvador de Jujuy in northern Argentina and Bolivian city of Tupiza when he crashed 50km from the finish line.

He was discovered injured on the ground by Portugese rider Paulo Goncalves, who lost time to alert race officials of his status.

“In Bolivia, in the final part of the special I stopped to help Toby Price, who was ahead of me and I found that he had been injured,” Goncalves said.

“I called and waited for the helicopter and I am confident that they will reinstate me with the time lost.”

Price started his title defence brightly by winning the second stage to claim the overall lead.

Having fallen 16 minutes off the pace with an error-ridden third stage, he was attempting to make up ground when he crashed on Thursday.

In 2016’s Dakar Rally, Price won the gruelling race almost 40 minutes ahead of his nearest rival.

It is not his first major crash, having broken his neck and back during a race four years ago.

Spaniard Joan Barreda, who retained the overall race lead after coming second in the fourth stage, expressed sympathy for Price.

“It is a shame what has happened to Toby Price,” he said.

“Hopefully it’s nothing too serious and he will get over it soon and be back at full speed on the track soon.”