Australian Rohan Dennis said his abrupt withdrawal from the Tour de France was the 'right decision' ahead of Friday's time-trial, the discipline at which he is world champion.

Dennis won the 2018 world time trial road race at Innsbruck in November, beating Dutch ace Tom Dumoulin and world one-hour track record holder Belgian Victor Campenaerts in third.

The 29-year-old from Adelaide also won the time-trial in June's Tour de Suisse, finishing the race second overall behind Colombia's Egan Bernal.

The Bahrain Merida rider threw in the towel at the start of the Peyresourde, the first of two climbs on Thursday's 12th stage, after he had been busy trying to make the early breakaway.

Dennis released a statement overnight Thursday in which he did not address the reasons for his withdrawal during the 12th stage on Thursday but suggested they were not physical.

"I am very disappointed to leave the race at this point," said Dennis, who has won stages on all three Grand Tours.

"The individual time-trial tomorrow (Friday) had been a big goal for me and the team, but given my current feeling it was the right decision to withdraw earlier today.

"I wish my teammates the very best for the remainder of the race and would like to thank all the Tour de France fans who cheered for me, at home and on the roadside, since Brussels."

"I will hopefully be back competing in this great race again over the coming seasons."

Gorazd Stangelj, the Bahrain Merida team's sports director, made an effort to persuade Dennis to continue the race but to no avail.

The team later released a statement saying "the welfare of all our riders is our key concern."

"He's the kind of guy who wants to have everything 100 percent and it's not easy to have everything 100 percent all the time," Stranjelj told reporters. "He's a special guy, let's say, all champions are."