The Frenchman was out riding near his home when he crashed while stretching. He sustaining fractures to his ribs, scapula (shoulder blade), and two vertebrae of the neck, as well as a pneumothorax (collapsed lung).
Groupama-FDJ announced the news on Saturday, adding that Roux will be off the bike for four to five weeks, at which point his condition will be re-evaluated.
Roux, 33, made his season bow at the UAE Tour, but was forced to abandon on the final stage to Palm Jumeirah after a heavy crash that left him suffering neck pains.
"A week after my fall at the UAE Tour I fell again but in training," Roux wrote in a post to Facebook on Sunday. "During this training outing I still had pain in my neck, so I wanted to stretch on the bike and unfortunately the bike went sideways, and I fell.
"Serious consequences this time: K1 and K2 fractures on the left, K1 fracture on the right with displacement, multiple fractures of the left scapula, non-displaced fractures of the C6 and C7 vertebrae, pneumothorax, perforation of the pleura."
It isn't the first time Roux has suffered a shoulder blade fracture during his 14-year pro career, having sustained the same injury after a camera motorbike caused a crash at the GP Bruno Beghelli in 2018.
He has been with Groupama-FDJ since turning pro back in 2008 and has 16 wins on his palmarès to date. His biggest career win came during his Grand Tour debut at the 2009 Vuelta a España, where he stuck it out in the break for 187 kilometres to hold off the sprinters by a handful of metres in Talavera de la Reina.
The 2018 French road race title and the 2011 editions of the Circuit de Lorraine and Circuit de la Sarthe rank among his other 15 pro wins.
Groupama-FDJ are currently competing at Paris-Nice, with David Gaudu leading the team and Arnaud Démare sprinting to second place on Sunday's opening stage. Thibaut Pinot will lead the team at Tirreno-Adriatico, which begins on Wednesday.
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