The 40 year-old is expected to be named Inverness Caley manager this week and Dons boss Jimmy Calderwood said: "He had a talk to them on Thursday night and I think he is going to talk to them on Monday. I expect to lose him to be honest."
The Dons boss praised "brilliant" Brewster's final contribution to the Dons.
"I think young (Chris) Hogg learned a lot playing against him," Calderwood said.
"We have got other players. Lee Miller was unlucky, he was brilliant at the end of the season. Steve Lovell is there and wee Chris Maguire is champing at the bit although he is a different type of player.
"That's why we brought 'Brew' in - to learn from him. We will see how it goes, there is still a bit of talking to be done."