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.

The Swiss squad’s top two title contenders, Alexandre Vinokourov and Andreas Kloeden, were injured in separate spills in the bumpy fifth stage Thursday through the Burgundy winemaking region. It wasn’t clear whether either man would take the start Friday.

Italy’s Filippo Pozzato won a sprint at the end of the 113-mile trek from Chablis to Autun, and Fabian Cancellara of Team CSC retained the race leader’s yellow jersey for a sixth day.

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

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

Leipheimer, a native of Butte, finished the day 63rd and is in 22nd place overall. He is 1 minute behind the leader.

Vinokourov, seen by many as the man to beat in this year’s Tour, tumbled off his bike with 15 miles left and had deep cuts in his knees. The Kazakh rider finished the stage 1:20 behind Cancellara, dropping to 81st place, 2:10 off the leader’s pace.

‘‘He’s a warrior in the tough moments, he becomes dangerous when he has a setback,’’ Astana sporting director Marc Biver said. The 33-year-old Vinokourov, who won the Spanish Vuelta last year, finished third in the 2003 Tour and fifth in 2005.

Kloeden, who was runner-up to Lance Armstrong in 2004 and third last year, sustained a hairline fracture in his tailbone after tumbling into a ditch with 45 miles left. He got up, stayed with the pack and held second place overall — 33 seconds behind Cancellara.

Spaniard Benjamin Noval of the Discovery Channel team crashed in the final descent with 4.8 miles to go. He was taken to a hospital for X-rays and stitches on deep cuts in his chin and on his right arm.

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, probes and admissions to shake cycling over the past year, and focus on the sporting drama of its showcase event.

Astana was disqualified last year on the eve of last year’s Tour after the names of five of its riders — though not including Vinokourov — turned up in the Spanish doping probe known as Operation Puerto.

Kloeden raced for T-Mobile last year. Since then, several former riders from the German team’s predecessor, Telekom, admitted to doping in the 1990s.

Former Telekom rider Eric Zabel, who captured the green jersey awarded to the Tour’s best sprinter on Thursday, admitted earlier this year to having used banned performance enhancer EPO once back then.

That admission, Zabel told France-2 TV, was ‘‘a little bit of a liberation for me, I’m now taking the race day-to-day. I’m happy again to be in the pack ... I thought for a moment that my career was over.’’

Pozzato said he toyed with the idea of urging his team, Liquigas, to wait up for Vinokourov, as fellow 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 (seven-time Tour winner Lance) Armstrong ... I always stayed 3 meters back and never got too close,’’ he added.

Cancellara, a time-trial specialist who won the prologue and Tuesday’s Stage 3, has said he expects to lose the coveted shirt once the race moves into the Alps starting Saturday.

‘‘I’m really tired now, that’s for sure,’’ he said, after his six-day run of clinging to the lead.