The defender joined Milan in the summer from Chievo Verona.
"He's made quite a leap from Serie B to Chievo and now to Milan, one of the most important clubs in the world," agent Andrea Cattoli told Itasportpress.
"He has the total backing of the Milan board and Vice President Adriano Galliani told me a few days ago that Acerbi was not for sale and would not leave in January.
"He's played some good games for Milan, but he needs time to demonstrate all of his qualities. He's part of the young project at the club."