he joined the club's academy ahead of the 2002–03 season. In his first season in the club's youth academy, he won the Division d'Honneur des 16 ans, the under-16 league title of the Bourgogne region. During the 2003–04 season, Diaby alternated between playing on the club's under-19 team in the Coupe Gambardella and playing in the club's reserve team in the Championnat de France amateur, the fourth level of French football. During the reserve team season, he played on the team alongside future Arsenal teammate Bacary Sagna, as well as Younès Kaboul, Hassan Yebda, Jean-Joël Perrier-Doumbé and former Clairefontaine classmate Garra Dembélé. Diaby finished the season with the team with 11 appearances and one goal as the team finished first in its group. After the season, he signed his first professional contract with the club agreeing to a three-year deal. Manager Guy Roux subsequently promoted Diaby to the first team and assigned him the number 24 shirt. 2004–2006 Similar to the previous season, Diaby regularly trained with the first team, while concurrently featuring as a starter on the club's reserve team. He made his professional debut on 14 August 2004 appearing as a substitute in a 3–1 league win over Rennes. After making his debut for the club, Diaby spent the rest of the fall season either playing on the club's reserve team or dealing with injuries. He returned to the team in March 2005 making his European debut in the team's UEFA Cup Round of 16 first leg tie against domestic rivals Lille. Diaby appeared in both legs as a substitute as Auxerre won the round 1–0 on aggregate. The club later lost in the quarter-finals to Russian club CSKA Moscow. Diaby made his first professional start on 20 March against his former youth club Paris Saint-Germain. He played 74 minutes before being substituted out in a 1–0 loss. Diaby made three more appearances as a substitute to close out the season. Following the season, Roux retired as manager of Auxerre after managing the club for 44 straight seasons. He was replaced with former France national team coach Jacques Santini. During the season, Diaby featured early on during the campaign, but as the season wore on, he struggled with injuries, which subsequently, led to the player failing to gain the confidence of Santini. Unlike fellow youngsters Sagna and Kaboul who were quickly establishing themselves at their respective positions, Diaby