In June 2005 he joined Nice but left after only two seasons to sign a four-year contract with Rennes, where he was viewed as a replacement for Dutch defender Mario Melchiot, who had departed for Premier League club Wigan Athletic. Fanni was named in the Ligue 1 Team of the Year for the 2008–09 season. He has expressed a desire to play in the Premier League and was strongly linked with a move to Newcastle United before signing for Rennes. Sky Sports 12 December 2008 He was also linked with EvertonSky Sports 6 October 2009 and West Ham UnitedSky Sports 4 June 2009 prior to signing a one year contract extension with Rennes in November 2009, which kept Fanni tied to Les Rouges et Noirs until June 2012.
In December 2010, Marseille successfully acquired the services of Fanni.