Giant-Alpecin tweeted that initial x-rays showed a fracture in Dumoulin's left radius, an injury that can take 40 days to recover from. The time trial that Dumoulin had his eye on is in just 19 days.
The Dutch rider, who won stages nine and 13 of this year's Tour, went down after clipping the wheels of the rider in front and losing control of his bike.
Dumoulin dominated the stage 13 time trial in the Ardèche, further lowering the odds on him winning the hilly race against the clock in Rio on August 10.
The Giant-Alpecin man beat Chris Froome by over a minute over the 37.5km route between Bourg-Saint-Andeol and Le Caverne de Pont d'Arc and admitted afterwards that the win would make him favourite for the Olympic Games.
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