Haroun made a dream start to his Middlesbrough career, scoring on his debut in a 3–1 win over Birmingham City on 21 August 2011. His first team start came three days later on 24 August 2011 when he helped Middlesbrough to a 2–0 victory over Peterborough United in the League Cup second round. Since making his debut, Haroun has been involved in a number of matches in the first team. Haroun scored his second goal for Middlesbrough in a 3–2 victory against Cardiff City on 17 December 2011. Despite being plagued with injuries throughout the 2011–12 season, he went on to make thirty–five appearances and scoring two times in all competitions.