 His first appearance of 2006–07 was in a 0–0 home draw with Peterborough United on 12 August 2006, a match he entered as a 59th-minute substitute.The next game he played in was a 4–1 victory away to Championship team Sheffield Wednesday in the League Cup on 23 August 2006.Mackin suffered a knee injury during a reserve-team match in September 2006 and made his return as a 90th-minute substitute in a 4–1 defeat after extra time away to Birmingham City of the Championship in the League Cup second round on 19 September.