Salahuddin made his International debut in football at Malaysia in 1975 at the Merdeka Cup. At the end of the tournament he and his fellow players came to know about the Assassination of Sheikh Mujib. Coming back to Dhaka Salahuddin saw Abahani devastated and decided to leave the country. So he accepted the proposal to play at the Hong Kong League. There he played for Caroline Hill FC for one season. He came back after playing a solitary season and rejoined Abahani. Kazi Salahuddin is the first ever Bangladeshi Football Player to have a Foreign Football Club Appearance as a Professional Football Player in Bangladesh Football History. In total he made thirty official appearances for the national team and scored 10 times in 1973 he scored against Thailand and also against Singapore. In 1975 merdeka football tournament he scored against Hong Kong, Thailand and against Myanmar. In 1979 Asian cup qualifiers he scored against Qatar in a 3–1 loss but ended up scoring the winning goal against Afghanistan in a 3-2 win which saw them qualify for the 1980 AFC Asian Cup. In the main tournament he scored a goal against North Korea in a narrow 3–2 loss. He also scored a hattrick against Malaysia.