Real Madrid made an approach for Balotelli last week, which was immediately rebuffed.
"Will Balotelli be sold? No, for the moment he won't go, but in football those who are not for sale sooner or later go on the market," agent Mino Raiola told the Corriere dello Sport.
"Milan have an important project in place with Mario and he is very happy here. You can be sure he won't move for now, but tomorrow... I don't know.
"It is very tough for Serie A to hold on to top players right now, as their revenue is only a third of what English or Spanish clubs make."