Cavendish, who topped the world in Copenhagen a year ago, suffered a bruised arm in the incident which is reported to have occurred near his Italian home in Quarrata, Tuscany.
Cavendish, who has joined Omega Pharma-Quick Step for 2013 after one season with Team Sky, tweeted: "Went & hit the back of a car that slammed on today [Monday] in training. Wasn't ideal. Apart from a bruised arm, I'm relatively ok. If anyone cares."
The incident occurred in the same month that Team Sky's Tour de France and Olympic gold medalist Bradley Wiggins and British Cycling and Sky's head coach Shane Sutton were involved in cycling crashes.
Sutton was taken to hospital after suffering a head injury in an accident 10 days ago, a day after London Olympics time trial champion Wiggins suffered a fractured rib, a bruised lung and a dislocated finger following a collision with a white van in Lancashire.
Australian Sutton had recovered sufficiently to help orchestrate Britain in the UCI track World Cup in Glasgow while Wiggins was back on his bike training after recovering from his injuries.