Diagne began his career with
Génération Foot in
Dakar before being scouted by
FC Metz in January 2007. In late August 2014, he joined
Stade Rennes from
SC Freiburg for a reported transfer fee of €1.5 million signing a three-year contract. In early July 2016, Diagne signed for
Werder Bremen. The transfer fee was estimated at €1.5 to 2 million. On 10 January 2017, Diagne joined
Ligue 1 club Metz on loan, rejoining his former club until the end of the
2017–18 season. In August 2018, Diagne joined
Süper Lig side
Konyaspor signing a two-year contract with the option of a third year. ==International career==