In total he made 450 appearances with the giallorossi, a record which lasted for 38 years, until 31 January 2007, when Francesco Totti played his 451st match for the club.

For this reason Roma's supporters understood that even if he was not Roman, he was a great example of how people from Rome love their team.

Losi made his first appearance in the Italy national team on 13 March 1960 in a friendly match loss (3–1) against Spain.

He was part of the squad that participated in the 1962 FIFA World Cup in Chile, playing two of the three matches of Italy.

[3] On 3 July 1968, Losi founded the Italian Footballers' Association (AIC), in Milan, along with several fellow footballers, such as Giacomo Bulgarelli, Sandro Mazzola, Ernesto Castano, Giancarlo De Sisti, and Gianni Rivera, as well as the recently retired Sergio Campana, also a lawyer, who was appointed president of the association.