The wide receiver, who has been recovering from an Achilles tear, was removed from the team's physically unable to perform list last week.
Kubiak told reporters: "He's been good. He practised today. I'm going to play him in the game. It'll probably be a brief appearance, but he needs to just get out there and get his feet wet so to speak.
"He'll probably play about 12 plays. Get hit. Get tackled. All that confidence he's been working on, just make sure he's ready to go. But he's good."
Posey sustained the injury during the team's playoff defeat to the New England Patriots earlier this year.