He played for the Chamonix Hockey Club who won the national championship in 1923, 1925, 1926, 1927, 1929, 1930, and 1931. Hassler helped France win the European Championship in 1924. He also played in the 1924, 1928, and 1936 Olympics. He was also a speed-skater. A trophy bearing his name is awarded to the best French player in the Ligue Magnus.