The Archbishop of Lyon, Cardinal Philippe Barbarin, is being questioned by police over allegations that he failed to act against a priest in his diocese accused of child sexual abuse.
The French Catholic Church has been hit by claims of covering up abuse, though the cardinal has repeatedly denied the allegations.
Pope Francis has approved measures to sack bishops who mishandle such cases.
But it is unclear if the decree will affect Cardinal Barbarin.
Police are investigating whether he failed to take action against a priest, Bernard Preynat, who is accused of abusing boy scouts between 1986 and 1991.
The cardinal walked into a police station at 08:00 (06:00 GMT) on Wednesday. He was questioned as part of a preliminary investigation, officials said, and was not taken into custody.