A patient who was treated for pneumonia near Paris on 27 December actually had the novel coronavirus, his doctor has said.
This would put the arrival of the virus a month earlier than currently thought.
Dr Yves Cohen said a sample taken from the patient at the time was recently tested and had come back positive for Covid-19.
The patient, who has now fully recovered, says he has no idea where he may have picked up the disease, as he had not travelled out of the country, something that suggests local transmission was occurring in France as early as December.
The source of infection could be his wife, who works at a supermarket close to the Paris airport.
A similar story has emerged from California in the United States where an autopsy of a patient showed that the first Covid death in the US was much earlier than originally believed.
This has significant implications for tracing the history of the spread of the virus, as well as for calculating the final death toll.