The Bees already had future Hall of Fame member, Al López, as well as future All-Star, Ray Mueller and veteran Johnny Riddle as catchers going into spring training in 1939 however, Masi impressed Bees' manager Casey Stengel so much that, Mueller and Riddle would be traded before the start of the season, leaving Masi as Lopez's backup. He made his major league debut with the Bees on April 23, 1939 at the age of 23. After his father died in 1942, he was given a 3-A draft classification exempting him from military duty as he was the sole support for his family.