Antonini had been mooted as a possible target for Premier League side Sunderland, but has now decided to join Genoa on a three-year deal.
He made over 100 appearances for Milan, scoring just one goal, since beginning his career at San Siro in 2000.
The 31-year old was loaned out to a series of clubs during his time with the Serie A outfit, including Sampdoria, Modena and Siena.
He became a particular favourite with coach Massimiliano Allegri, who installed him as first choice left-back for the 2010-11 season, where he helped his side to their 18th league title.
In an emotional tweet, he told fans: “After 23 years in Rossonero, today I salute the team I support. The time has come for me to go. Goodbye my Milan, I gave my heart for you. Thank you for everything.” as reported by Indo Eleven.
Source : www.indo11.com