After a difficult first season with the capitoline club, Mexès began the 2005–06 campaign on the bench. Roma's transfer misconduct in the purchase of Mexès led to the club's being suspended in 2005 from signing players other than free agents, but the ban temporarily lifted in August. As the club did not sign anyone due to the ban, he became a key player for Luciano Spalletti's squad. Mexès played nine out of a possible ten games for Roma in UEFA Cup competitions. He also played in the final of 2005–06 Coppa Italia. The "Giallorossi" finished fifth in Serie A, initially qualifying only for the next year's UEFA Cup, but due to the 2006 Italian football scandal, Roma were awarded second, allowing Mexès to play for the first time in the UEFA Champions League.