 In 1942 Cassel auditioned for the Metropolitan Opera and was invited by Edward Johnson to join the roster of singers at the company.He made his debut with the company earlier than expected, replacing an ailing singer at the last minute in the role of Bretigny in Jules Massenet's "Manon" on December 12, 1942 with Bidu Sayão in the title role.He continued to sing at the Met through the Spring of 1945 in mainly comprimario roles like Count Ceprano in Giuseppe Verdi's "Rigoletto", the Gypsy in Verdi's "Il trovatore", Hermann in Jacques Offenbach's "The Tales of Hoffmann", and the Philosopher in Gustave Charpentier's "Louise".