Starting his career in Arvidstorps IK, Hassan moved north in 2002 to Borås and IF Elfsborg. He had to wait until 2005 before making his debut for the club. When first choice goalkeeper Johan Wiland got injured, he played well enough to place Håkan Svensson, who had been brought in as a short-time replacement for the injured Wiland, on the bench. During the pre-season 2006 he became injured and Wiland reclaimed his place as first choice. In early 2008 Hassan was on trial with the English club Manchester City. Before the start of the 2009 season it was believed that he would replace Wiland who had left for Copenhagen, however the arrival of Australian goalkeeper Ante Čović and Swedish Joakim Wulff saw Hassan becoming third choice and he started to openly state that he wanted to leave the club. On 9 July, it was confirmed that Hassan would leave IF Elfsborg and move to the Danish side Aalborg BK, signing a one-year loan contract. On 29 June, he joined the Swedish Superettan club IFK Norrköping on a short term contract to replace the injured goalkeeper David Nilsson. On Friday 27 August, he made his debut in Superettan for IFK Norrköping against Ljungskile SK when he replaced goalkeeper Niklas Westberg who had received a one match suspension for his three yellow cards. The match ended 2–1 to IFK Norrköping. In December 2010 he signed a 3-year contract with IFK Norrköping after the club got promoted to Allsvenskan and formally left IF Elfsborg. On 6 February 2013, Abbas returned to 2012 Swedish champions IF Elfsborg, after breaking his contract with IFK Norrköping. Replacing Andreas Andersson who left as a Bosman from Elfsborg to Ljungskile SK.
International career
Hassan has played his first game with the Lebanese national team against Iraq on 22 January 2012. Abbas' star moment for Lebanon was the game against Iran, where he was man of the match, and helped his team to win, 1–0. Selected and promoted by German goalkeeper coach Christian Schweichler and coach Theo Bücker, he was in inspired form throughout the 90 minutes, produced a string of fine acrobatic saves in the closing stages as Iran threw everything forward, which forced Iran coach Carlos Queiroz to quote "I think a national hero was born today. For me the score was Abbas Hassan 1 Iran 0." Later, his skills also helped the team during the match against South Korea, until Kim Chi-Woo equalized in 97'.
