Brissett suffered a sprained left MCL in Sunday's loss to the Steelers, Mike Chappell of Fox 59 News Indianapolis reports.
Per the report, the Colts are still waiting for Brissett's full MRI results and have not yet ruled the quarterback out for the Week 10 game against the Dolphins. At this stage, however, it looks like there's a solid chance that Brian Hoyer will start that contest.