[2] Muzzi started his career with AS Roma, making his debut in Serie A on 11 February 1990, in a league match against Inter ended in a 1–1 tie, and scoring his first goal the following season.

He then returned to Rome to join Lazio for the 2003–04 season; although he was not a regular first-team member, his performances often proved to be decisive on the pitch, as shown by his goal which enabled Lazio to avoid relegation during the 2004–05 season; during his time with the club, he won the 2003–04 Coppa Italia, also reaching the semi-finals of the 2003–04 UEFA Cup, but missed out on the 2004 Supercoppa Italiana to Milan.

[2] In September 2006, at the age of 35, and after having turned down a youth coach role at Torino, he agreed a two-year contract with Serie C1's Padova.

[7] In July 2022, Cagliari appointed Muzzi as director of football alongside Stefano Capozucca and dealing with organizational and management matters within the first team squad.

[9] Following the appointment of Claudio Ranieri as new head coach, Muzzi filled in for a single game, a 2–0 win against Cosenza, although he could not serve from the dugout and had to be replaced by Fabio Pisacane due to him being sick.