Based on what Doc says, it isn't looking good for Darius Miles. From the Herald:

Neither Darius Miles nor rookie J.R. Giddens played Friday night. That’s not a good sign for either player - especially the non-guaranteed Miles - considering that Rivers is now working his rotation players into regular-season form.

Rivers acknowledged that he may cut a player soon from his 16-man roster, though the deadline is not until Oct. 27.

Asked if he had learned enough about Miles, Rivers chose to speak of the group at the end of his bench instead.

“We’re still learning about three or four guys,” Rivers said. “But someone is not going to make this team who is good enough to make an NBA roster. It’s not an easy decision, but I would like to do it sooner than later.

“I’m not sure yet, honestly. We could go to the last day, but I want to give someone a chance (to sign with another team) when we make the decision.”

It's Ainge who ultimately makes the decision, but with Miles being the guy without a guaranteed contract, and not showing a whole lot in the preseason, odds are it'll be him.