Kammala jumla mai zuwa: An haife shi a Muzzana del Turgnano, Frossi ya fara aikinsa a matsayin ƙwararren ɗan wasan ƙwallon ƙafa tare da Udinese, kuma, bayan dogon zama a Serie B (tare da Padova, Bari, da L'Aquila), Ambrosiana Inter ce ta saye shi, inda ya fara bugawa a ranar 21 ga Yuni, 1936, a gasar Mitropa. Bayan haka, Vittorio Pozzo, kocin ƙungiyar Italiya, ya kira Frossi don wasannin Olympics na 1936, yana jagorantar ƙungiyar zuwa nasarar gasar tare da nasarorin da ya samu. A cikin shekaru masu zuwa, Frossi ya buga wa Inter wasa daga 1936 zuwa 1942, ya lashe <unk>Scudetto<unk> ko gasar zakarun Turai, sau biyu a cikin
1938 da 1940, da kuma Coppa Italia a 1939. Ya zira kwallaye 49 a wasanni 147 tare da Inter, 40 daga cikinsu sun zo a gasar, a cikin wasanni 125. A lokacin Yaƙin Duniya na II, daga baya kuma ya buga wa Pro Patria tsakanin 1942 da 1943, da Como a 1945, kafin ya yi ritaya.