The Rossoneri swooped to take Balotelli back to Serie A in January after reaching an agreement with Manchester City for the former Inter Milan forward.
He has settled quickly back at San Siro, netting 12 times in 13 appearances during the second half of the 2012/13 campaign.
Balotelli has quickly become a fans' favourite, as much for his antics off the field as on it, and Galliani claims he can already claim to be an 'icon' in Italian football.
At just 22 years of age it remains to be seen how long the fiery frontman will stick around in Milan, but it has been made clear to any potential suitors that they would need to piece together a record-breaking transfer package in order to secure his services.
Galliani said of Balotelli: "He's absolutely untransferable. He is our icon.
"The only way that changes is if someone arrived with an offer of €150million (£129m) and you can't refuse."
Galliani has also been discussing the future of Urby Emanuelson - who spent the second half of last season on loan at Fulham - and Robinho, who could return to Santos this summer and free up space for another forward to come in.
He added: "There are lots of negotiations opened. Emanuelson could stay. We will talk with him and the coach.
"Robinho? We have made our last request and have gone under €10million. We can't go any lower.
"If he leaves, we will sign another young striker. (Fiorentina's Adem) Ljajic is in our thoughts, (Keisuke) Honda too. I don't know if we will buy Ljajic or someone else. We definitely won't be buying a striker aged 32."