In 2004, El-Masri became a member of SG Neukölln swimming club in Berlin, and also, trained for the German national team. However, he decided to compete instead for the Syrian Olympic team at the 2004 Summer Olympics in Athens. He qualified for the men's 50 m freestyle event, and swam in the eighth heat against four other competitors including Croatia's Duje Draganja, who eventually won the silver medal in this event. El-Masri finished in fourth place of his assigned heat, with an impressive time of 22.58 seconds. He nearly missed out of the semi-final rounds, as he placed eighteenth in the overall rankings, tying his position with two-time Olympic championAlexander Popov of Russia, and Johan Kenkhuis of the Netherlands. El-Masri continued to compete for Syria at two FINA World Championships, but failed to reach his personal best times set at the Olympics. He also won a gold medal for the men's 50 m freestyle at the 2006 Asian Games in Doha, Qatar, with an impressive time of 22.41 seconds, just ahead of Japan's Makoto Ito, and China's Cai Li.
Germany (2008–present)
Having won the gold medal at the Asian Games, El-Masri made certain doubts in his decision if he could swim for either Syria or Germany, because of his dual citizenship. In 2008, he qualified for the Summer Olympics in Beijing, after finishing second in the 50 m freestyle event at German national trials, just behind Steffen Deibler, with a time of 21.80 seconds. Shortly before the games, El-Masri was given a chance by FINA to switch nationalities, after having represented his country of origin at the previous Olympics, and at the World Championships. Representing his adopted nation Germany, El-Masri competed in the men's 50 m freestyle, along with his compatriot Deibler, who finished ahead of him in the trials. He challenged seven other swimmers on the twelfth heat, including heavy favorites Amaury Leveaux of France and three-time Olympian Stefan Nystrand of Sweden. El-Masri finished behind U.S. swimmer Ben Wildman-Tobriner in fourth place by 0.21 of a second with a time of 21.96 seconds. El-Masri recorded a tenth fastest time in the preliminary heats to advance further into the semifinals. The following morning, El-Masri fell short in his bid for the final, as he finished the semifinal run with a third slowest time of 22.09 seconds.