 Khalfan started out with Al-Arabi (his father's club) and was signed by Al-Sadd in 2004.He assimilated into Al Sadd's first team at the age of 17 in March 2005, under head coach Doru Isac scoring against Al-Shamal.2005–06 was a significantly improved season for him when he scored goals in the Qatar League, Crown Prince Cup and Asian Champions League.