The 23-year-old, who returned to Serie A from Manchester City in January 2013, has come under criticism from the Italian press for some of his performances in recent weeks.
Balotelli has been linked with a Premier League return on numerous occasions and Jose Mourinho fuelled talk of a switch to Chelsea after speaking of his desire to manage the striker again.
However, Galliani insists that the Italy international is still highly regarded at the San Siro and that he is happy in Milan.
"He has never felt badly here," said Galliani.
"I repeat, some people forget how much he helped us last season achieving Champions League qualification.
"He's been here a year and two months and he has a really high efficiency that is liked by the club."
Meanwhile, Galliani remained coy on the future of Brazilian star Kaka, with Milan's lack of Champions League football next season casting doubts over whether he will stay.
He added: "About Kaka, I don't think there is anything else to say. He had a deal known to everyone and there is nothing new.
Galliani also says he will wait to address the situations of loan duo Adil Rami and Adel Taarabt as they are set to return to their parent clubs, Valencia and QPR respectively, during the summer.
"In May, at the end of the league, we will discuss Rami and Taarabt's situations. Some (offers) are clear and already on the table," he said.