Froome (Team Sky) today posted an image of a bent and broken bike to his 1.2 million Twitter and over half a million Facebook followers, saying the incident was a hit and run.
Team Sky said the Monaco-based Froome had continued his training session after returning home to get a spare bike.
He is training for June's Criterium du Dauphine, his familiar warm-up event before the Tour de France between July 1-23. He is favourite to win the event for a third successive year.
The incident comes only two weeks after the death of 2011 Giro d'Italia winner Michele Scarponi (Astana) who was run over by a motorist when training near his home in Filottrano, Italy.