The striker has been linked with several Premier League sides in recent weeks.
The young forward has been strongly linked with a move away from the Hawthorn at some point, with a number of clubs thought to be interested in his services.
An exit seems likely as well, with him also having fallen down the pecking order at the club in recent weeks following a falling out with manager Tony Pulis.
Mills though, doesn’t believe that he will leave any time soon, saying that his stock has seriously fallen since the summer.
"I'd be surprised if Berahino left,” he told BBC Sport.
“Without a shadow of a doubt, his stock has fallen, and his price has fallen with it. He was worth £25 million - he's now worth 12 - 15 at most now.”
"I think Tony Pulis will happily say to other managers - 'he's not easy to control, this kid. He will cause problems.'"
While Berahino has been far from impressive this season, there is still every chance that someone may take a punt on him in January.
Everyone is chasing a goalscorer in this window, and he has proven he can score goals in the Premier League before now.
He is only 22-years-old as well, meaning he still has plenty of time to develop and improve, and any prospective clubs may feel £12-15m is a good price to secure him this month.