On 1 May, Diaby suffered a severe ankle fracture after being on the receiving end of a tackle, described by the media as "horrendous", from Sunderland defender Dan Smith. After the match, Wenger described the tackle as "a bad kick and an unnecessary one" and also criticized his competitors' over-physicality, while interim Sunderland manager Kevin Ball defended Smith stating "Smith is not a malicious, dirty player and I think it's unfair to make that call on him and say he deliberately went to do it. Dan went for the ball, unfortunately Diaby was quicker than him". As a result of the injury, Diaby missed the 2006 UEFA Champions League Final, as well as the 2006 UEFA European Under-21 Football Championship. He underwent three surgeries to repair the injury and was told by doctors that the injury could possibly be career-ending. Following the surgeries, he underwent eight months of rehabilitation and made his return to first team action in the 2006–07 season in a League Cup match against Liverpool. He appeared as a substitute in the match as Arsenal won 6–3. On 25 February 2007, while participating in the 2007 Football League Cup Final against Chelsea, Diaby, while attempting to clear the ball out of the Arsenal defense, accidentally kicked rival defender John Terry in the face. Unconscious, Terry was stretchered off and hospitalized, but recovered to return to the Millennium Stadium in Cardiff for the trophy presentation following Chelsea's 2–1 win. Though Arsenal lost, Diaby was credited with an assist on the team's only goal of the match, which was converted by Theo Walcott. Diaby scored his first and only goal of the campaign on 14 March in a 1–0 win over Aston Villa when he deflected in a Júlio Baptista shot. He remained a fixture within the team for the rest of the campaign, mostly as a substitute as he only started in consecutive matches once.