Le Havre defender Samba Diop has died at the age of 18.
The French second division club announced the news with “great sadness” on Saturday, without stating the cause of Diop’s death.
Their Ligue 2 match with Reims – scheduled to take place later on Saturday – has been postponed.
The French football league has asked that all clubs in the country’s top two divisions observe a minute’s silence before matches this weekend.
A club statement said: “This is a horrible moment for all the players, staff members, volunteers, administrators and leaders.”
Diop had played 21 times for the club’s B team this season in the fourth tier of French football.
Several young players have died suddenly in recent years, commonly of cardiac problems.
Fellow 18-year-old French defender Thomas Rodriguez, who played for Tours, died in March.