Balotelli's future at the San Siro has been the subject of speculation in recent weeks after an indifferent run of form.
The former Manchester City striker missed a penalty in the weekend draw with Genoa and then reportedly turned up late for training two days in a row to fuel rumours about his future.
Galliani was in the dark about the reported training incidents, but insists Balotelli will stay at the club.
"I don't know anything about it," said Galliani. "Training was at 11.30, he got there before 11. I don't know what time they were supposed to meet up - you'll have to ask the coach.
"Is Balotelli unhappy? He will stay, I'm 101 per cent certain about that. He's our centre-forward, it's just one of those moments."
Galliani also revealed Stephan El Shaarawy will be staying at Milan after he rejected an approach from a mystery club for the forward.
"El Shaarawy is staying as well," he added. "A famous Italian coach who works abroad rang me up to ask for him and I politely said no."
Galliani went on to reveal that Milan are hoping to sign a defender and a winger during the January transfer window.
"We have very clear ideas about the transfer window," noted Galliani.
"We're looking for a defender and a wide attacker."