The former Ghana international was indefinitely suspended by the Gelsenkirchen club, along with Sydney Sam, for indiscipline back in June.
He has been training with Milan in recent months in order to retain fitness, but is still under contract at the Veltins-Arena.
Despite having featured in a friendly for the Rossoneri, Crnjar insists there has been no talks about a deal with Milan.
"Dr Galliani and coach Mihajlovic gave us this opportunity and we are grateful. In January we will decide what to do but for now there is no news.
"If he would like to play for Milan? Yes, no doubt Boateng has this desire, but it is really too early to make any kind of reasoning. We'll see what happens in January."