The pack rides through sunflower fields near Bazoches during the fifth stage of the Tour de France. Thursday's stage ran between Chablis and Autun, France.

Autun, France ? Team Astana missed last year’s Tour de France over a doping probe. Now, its star riders have another problem: crashes on the course.

Alexandre Vinokourov and Andreas Kloeden, the Swiss squad’s top two title contenders, were injured in separate nasty spills Thursday in a bumpy sixth stage through the Burgundy winemaking region.

It wasn’t clear whether either would start today.

Kloeden had a hairline fracture in his tailbone after tumbling into a ditch, and Vinokourov, who fell with 15 miles to go, had deep cuts in his knees.

Vinokourov dropped from 12th overall to 81st place, 2:10 off the pace of race leader Fabian Cancellara of Team CSC, who retained the yellow jersey for a sixth day.

Italy’s Filippo Pozzato took the stage, with a sprint at the end of the 113-mile trek from Chablis to Autun.

Even if Vinokourov and Kloeden join the pack for today’s mostly flat 124-mile ride from Semur-en-Auxois to Bourg-en-Bresse, the injuries could make them vulnerable to attacks and shake up the cast of race favorites.

Their woes could give an opening to contenders such as American Levi Leipheimer, Australia’s Cadel Evans, Spaniards Alejandro Valverde and Oscar Pereiro, and Russia’s Denis Menchov.

Vinokourov, seen by many as the cyclist to beat, tumbled off his bike with 15 miles to go and finished the stage 1:20 behind Cancellara.

“He’s warrior in the tough moments,” said Astana sporting director Marc Biver of the 33-year-old, who finished third in the 2003 Tour and fifth in 2005. “He becomes dangerous when he has a setback.”

Kloeden, too, is dangerous.

After landing in the ditch with 45 miles to go, he got up, stayed with the pack and held second place overall – just 33 seconds behind Cancellara.

Stage winner Pozzato moved to third overall, winning a sprint ahead of Oscar Freire of Spain in second and Daniele Bennati of Italy in third. They and the main pack finished in 4:39:01.

The Tour is trying to get past a string of doping allegations, investigations and admissions and focus instead on the sporting drama of its showcase event.

Last year, Astana was disqualified on the eve of the Tour after five of its riders – not including Vinokourov – were linked to Operation Puerto, a Spanish doping investigation. This year, team CSC sporting director Bjarne Riis is skipping the race after admitting he used EPO on way to winning the Tour in 1996.

With so many familiar names, including last year’s champion Floyd Landis, missing, much has changed on the Tour.

On Thursday, Pozzato said he toyed with the idea of urging his team, Liquigas, to wait for Vinokourov, as riders might have done during the era of seven-time Tour winner Lance Armstrong.

“When I knew that Vinokourov had fallen, I was tempted to ask my team to slow down and wait for him,” Pozzato said. “Maybe there is less respect for the big riders than there once was.”

“When I started in cycling there was a very clear hierarchy, and I was afraid to get too close to Armstrong. … I always stayed 3 meters back and never got too close.”

American cyclist Christian Vandevelde, who was pushing the pace along with the Liquigas riders, took issue with Pozzato. Vandevelde said was not informed of Vinokourov’s woes, and besides, the Kazakh star was not in the lead.

“If the yellow jersey had crashed and we knew about it, it would have been a different story,” Vandevelde said. “Lance would have been in the yellow jersey.”

That coveted shirt might soon have a new owner in this edition of the Tour.

Cancellara, a time-trial specialist who won the prologue and Tuesday’s third stage, has said he expects to lose the yellow jersey once the race moves into the Alps on Saturday.

“I’m really tired now, that’s for sure,” he said, after six days of clinging to the lead.