He had been listed as probable most of this week after returning last weekend after in-season knee surgery, but team doctors found swelling in the knee Saturday.
Team officials now say Brown will be re-evaluated before Indy (4-3) turns in its list of inactive players 90 minutes before kickoff. If Brown does not play, rookie Vick Ballard likely would see the bulk of the action. Ballard has started Indy's past three games.
The Colts host Miami (4-3) in a matchup between teams that have surprised everyone by starting rookie quarterbacks and managing to spur talk of playoff hopes among their fans this season. Game time is 1 p.m. ET.