Image 1 of 3 Fabian Cancellara (Radioshack) showed he was back to full form after his troubled 2012 season (Image credit: Bettini Photo) Image 2 of 3 Fabian Cancellara (RadioShack - Leopard) pushes Sep Vanmarcke (Blanco) to the limit (Image credit: Bettini Photo) Image 3 of 3 Chris Horner (RadioShack) (Image credit: Bettini Photo)

RadioShack Leopard will be without two key riders for the upcoming Tour de France as both Fabian Cancellara and Chris Horner today revealed they would not be part of the team's roster when the French Grand Tour kicks off on Saturday, June 29 on Corsica.

Horner has been sidelined for much of the season by an injury in his left knee, iliotibial band friction syndrome, which was sustained near the conclusion of Tirreno-Adriatico in March, where Horner finished sixth overall. Six days later Horner started the Volta a Catalunya but only rode the opening stage on March 18 and withdrew the following day. The 41-year-old American has not competed since as his injury has repeatedly flared up in training following periods of recovery. After he was ruled out of the Amgen Tour of California Horner underwent knee surgery in the United States two weeks ago.

"It all hurts as I was so good in the early season," said Horner prior to the Tour of California. "In Tirreno-Adriatico I was as good as the best riders in the world."

Horner now hopes to salvage his season with a start at the Tour of Utah (August 6-11) followed by the Vuelta a España, which begins on August 24.

Cancellara's absence from the Tour will be a heavy blow for RadioShack Leopard. The Swiss powerhouse was the shining light in last year's Tour for RadioShack after he won the prologue time trial in Liège, Belgium and held the maillot jaune through the stage 7 where Bradley Wiggins took over the overall lead.

"So from now on it is officially that i will not riding the #TourdeFrance13 i will take other option and set up different races," Cancellara wrote on Twitter today, ending earlier speculation which arose during the recent Tour of Belgium about his participation in the Tour.

“My ambitions now are for later in the season, for the World championships," he said later in a press release. "Because of this I won’t be part of the Tour de France this time. I will have another program. That’s why I can now follow other goals. You have to go to races 100% motivated and that’s why I’m looking forward to the Tour of Austria, Poland, the Vuelta and to be 100% fresh for worlds."

While there's no prologue time trial at the 2013 Tour, there is a key test against the clock early in the Tour with a 25km team time trial in Nice on stage 4. Lacking Cancellara's time trial prowess, RadioShack Leopard's GC aspirations may take an early hit without his presence in the line-up.