Born in Monfalcone, Gerzeli, a winger, inside forward and centre-forward, started his career in the Serie C side C.R.D.A. Monfalcone, which was the team of his hometown Monfalcone. After World War II, Gerzeli played the 1945-46 Serie C season for Monfalconese (which was the new name of C.R.D.A. Monfalcone); he was then signed by Venezia, a team which was competing in the Serie A. Gerzeli only played one match during the 1946–47 Serie A season, on July 6, 1947 against Triestina. After this one-match experience, he left Venezia and moved to Marzotto Valdagno, coming back to Serie C. He played a Serie B championship in 1948-1949 with Salernitana. In 1952 he decided to leave Italy for Colombia, a nation in which professional football was well-paid because of the so-called "El Dorado" period. He played for Deportivo Samarios in Colombia along with two other Italian footballers, Corrado Contin and Alessandro Adam. He collected 20 appearances with Samarios, scoring five goals (the first of which was scored against Atlético Nacional on June 1, 1952). In the summer of 1954 he played in the National Soccer League (NSL) with Toronto Hungarians. In 1956, he continued playing in the NSL with Toronto Sparta, and was suspended by the league until 1960 after an incident with a referee in late 1958. In 1963, he served as a player-coach for K.F.C. Estonia in the National Soccer League.