At the start of the 2005–06 season, Haroun made his UEFA Cup debut, coming on as a 69th minutes substitute, in a 3–0 win against Liepājas Metalurgs to progress through to the next round. He made another UEFA Cup appearance in a 2–2 draw against Litex Lovech, but Genk were eliminated in a return leg after losing 1–0. However, Haroun spent the first three months placed on the substitute bench, having played four matches around this time. By October, he found his playing time, mostly coming on from the substitute bench in a number of matches. Haroun signed a contract extension with the club. At the end of the 2005–06 season, he made twenty–two appearances in all competitions.