A patient treated in a hospital near Paris on 27 December for suspected pneumonia actually had the coronavirus, his doctor has said.
This means the virus may have arrived in Europe almost a month earlier than previously thought.
Dr Yves Cohen said a swab taken at the time was recently tested, and came back positive for Covid-19.
The patient, who has since recovered, said he had no idea where he caught the virus as he had not traveled abroad.
Knowing who was the first case is key to understanding how the virus spread.
The World Health Organization (WHO) says it is possible more early cases will come to light, and spokesman Christian Lindmeier urged countries to check records for similar cases in order to gain a clearer picture of the outbreak.
The French health ministry said that the government was obtaining confirmation on the case and that it would consider further investigations if they proved necessary.
France is not the only country where subsequent testing points to earlier cases.
Two weeks ago, a post-mortem examination carried out in California revealed that the first coronavirus-related death in the US was almost a month earlier than previously thought.
