Balotelli sealed a transfer to the Reds in a deal believed to be worth £16 million on Monday, just 18 months after leaving England for San Siro.
Despite the 24-year-old's often-inconsistent displays and controversial off-the-field behaviour, Milan are grateful to the striker for his efforts during his brief return spell in Italy and wish him well for the future.
"We worked well together, Mario. We've been happy to have had you here and for this we say goodbye and thank you," read a statement on the club's official website.
"In one year and a half you've achieved a lot. You were decisive in our qualification for the Champions League in 2013 and were our top scorer last season. This is what your Milan thinks of you and this is our chance to confirm it publicly.
"There have been lots of memorable moments: the goalscoring debut versus Udinese, that late winner versus Torino at San Siro in May last year, the decisive goal against Siena and the screamer against Bologna on Valentine's Day at San Siro.
"Thank you for everything and for what you have done at the club. We wish you the very best of luck for your next sporting and professional adventure."