Kammala jumla mai zuwa: Guarnieri ya fara aikinsa na matasa tare da Codogna, kuma ya fara buga wasan ƙwallon ƙafa na Como a 1957, kuma ya buga wa Internazionale, Bologna, Napoli, kuma ya ƙare aikinsa tare da Cremonese 1973. Ya fi dacewa da dan wasan kungiyar Inter Milan da aka fi sani da La Grande Inter a karkashin kocin Helenio Herrera, tsakanin 1958 zuwa 1967, a takaice ya koma kungiyar don yin wasanni 3 a lokacin kakar wasa ta 1969-70. Ya kasance wani ɓangare na nasarar cin Kofin Zakarun Turai na Inter a 1964 da 1965, kuma ya lashe taken Serie A guda uku, da Kofin Intercontinental guda biyu a
1964 da kuma 1965. Kodayake bai sami damar lashe Coppa Italia ba a cikin aikinsa, ya kai wasan karshe a lokacin kakar 1964-65, ya rasa kusan sau uku tare da Inter.