Fattori was born in San Michele Extra, Verona. After having been a player for Audace San Michele, which later gave rise to Mariolino Corso, Fattori moved to Vicenza, making his Serie A debut as the club's starting defensive midfielder. In 1946 he went to Sampdoria, which acquired him (along with Bassetto) for a record 10 million lira after exhaustive bargaining with Inter. He would get to Inter in the summer of 1947 after only 12 months with Sampdoria. With Inter, Fattori would stay for seven seasons winning two championships in 1953 and 1954.