Vaughan has suffered a broken thumb, Mark kaboly of the Pittsburgh Tribune-Review reports.
The injury likely occurred in Thursday's matchup with the Eagles. Vaughan completed 7 of 13 passes for 67 yards in the contest. The 25-year-old already figured to be a long shot at making the final roster, as he projects as the fourth string quarterback on the team's depth chart. The Steelers also signed quarterback Bryn Renner on Saturday, which does not bode well for Vaughan's chances of making the roster.