"I sensed the thing straight away. When the kick came, I protected my ribs with my forearm. It's then that I got out of the car."
Despite the incident Barthez has said he wants to play on for two more years.
"It's out of the question (to retire)," Barthez said in Thursday's edition of L'Equipe.
"I tell myself my legs are good for another two years."
Nantes are bottom of the Ligue 1 table with 30 points - eight behind second-bottom Nice.
Barthez, a World Cup and European Championship winner with France, has made costly errors in recent matches and was booed and jeered by some Nantes fans during Saturday's game.
Having quit Nantes, the 35-year-old is now open to offers from other clubs.
"I'm not going to play for Nantes again," he said.
"I don't feel ready to live like that," said the keeper, who has won 87 caps for France,
Barthez, who only arrived only during the winter transfer window, said: "I don't feel safe there and I'd just prefer to leave."
Nantes succumbed to a 2-0 home defeat to Rennes on Saturday, and after just five minutes into the match, Barthez became the target of insults from sections of the Nantes support.
Barthez, 35, has been unsettled since joining Nantes in January and been accused on several occasions of feigning injury to avoid training.
In his 14 matches with the club, the former Marseille and Manchester United keeper has conceded 23 goals.