Police say they are trying to trace a spectator in connection with a multi-rider pile-up during the first stage of the Tour de France on Saturday.
The female spectator was spotted leaning into the path of the speeding peloton, holding a sign, in the Finistère region of Brittany.
German rider Tony Martin brushed into the sign and fell to the ground, with others behind him following suit.
Police say they have launched a criminal investigation.
They aim to charge the woman with "deliberately violating safety regulations and causing injuries that might prevent someone working for up to three months".
Video footage of the incident has been widely shared online.
The woman, wearing a yellow coat, can be seen holding a sign with "granny and granddad" written in German. She is looking away from the peloton coming towards her and does not see them approach.
One rider has had to pull out of the Tour completely and another eight riders were treated by an official doctor.
According to police, the woman fled the scene after the crash. Investigators have appealed for witnesses to get in touch.
Tour de France Deputy Director Pierre-Yves Thouault said the tour would take legal action against the woman.
"We are suing this woman who behaved so badly. We are doing this so that the tiny minority of people who do this do not spoil the show for everyone," he told AFP news agency.
France has relaxed its coronavirus restrictions and many people have flocked to see the riders.
Those hoping to watch the riders have been told to keep off the route and maintain their distance.
Following the crash, the Tour de France wrote on Twitter: "For the Tour to be a success, respect the safety of the riders! Don't risk everything for a photo or to get on television!"