 Riou was a member Lyon's first team since 2003, but failed to make his Ligue 1 debut for the club and moved to Lorient on a one-season loan in July 2006.He made his Ligue 1 debut on 4 November 2006 in the Lorient's 1–0 away victory over Olympique de Marseille.In July 2007, he moved to Auxerre on a four-year contract, making his Ligue 1 debut for the club on 18 August 2007 in their 1–0 home victory over Caen.