As promised by Wenger, Clichy began the season on the club's senior team primarily as the backup to England international Ashley Cole. He made his club debut on 28 October 2003 alongside fellow débutant Cesc Fàbregas in a League Cup encounter with Rotherham United. Arsenal won the tie 9–8 on penalties with Clichy converting his spot kick. On 22 November, Clichy made his league debut in a 3–0 win over Birmingham City. Following an injury to Cole in December, Clichy appeared in nine straight matches; six of them as a starter. On 24 February 2004, he made his UEFA Champions League debut in the first leg of the team's 3–2 knockout round victory over Spanish club Celta de Vigo. Clichy finished the campaign appearing in seven more matches. On 9 May 2004, he appeared as a substitute in Arsenal's 1–0 league win over Fulham. A week later, Clichy appeared on the bench in the team's final league match of the season; a 2–1 win over Leicester City. The victory assured Arsenal an undefeated league season, which resulted in the club becoming the second first division team in English football history to finish a league season unbeaten. As a result of the title, at 18 years and 10 months, Clichy became the youngest player to win a Premier League medal.