The paper said Le Drian, a member of the current Socialist government, would explain his decision at a meeting of the regional Brittany assembly later in the day.
Le Drian is considered as one of the more popular members of President Francois Hollande's cabinet and a respected voice in security matters and foreign affairs, and his support for the 39-year old former economy minister would give Macron more weight in those particular areas. (Reporting by Sudip Kar-Gupta; Editing by Michel Rose)