Rashean Mathis leaves field for Detroit*

DETROIT -- Detroit Lions cornerback Rashean Mathis walked off the field under his own power in the first quarter, but spent a bunch of time talking with trainers with his helmet off on the sideline.

Mathis, one of the Lions' starters at corner, was replaced by rookie Darius Slay -- the player Mathis replaced in the starting lineup last week.

It appeared as if the doctors and trainers were performing a concussion test on the 11-year veteran who signed last month after playing the first 10 years of his career with Jacksonville.

*Update: Mathis is going to be re-evaluated at halftime for a possible head injury (concussion).