Mussing came to St. George via the localTweed Heads rugby league club in 1945. He made an immediate impact at the Dragons as a blockbusting try scorer. He was the club's top try scorer in his debut year, and was immensely popular with the fans. The following year, Mussing was one of the major contributors to the club's fantastic season, although he missed the 1946 Grand Final after suffering a broken collar-bone in the second last club game of the year. His place in the team was ultimately given to the young local junior Chick Donnelley. Mussing stayed with the club for the 1947 season, before returning to Queensland in 1948 to play for the Fingal All Blacks.