Mathis sat out Jacksonville's game at Tennessee earlier this month because of a broken index finger on his left hand. Safety Reggie Nelson started in his place, missed several tackles and got beat for a touchdown in a 30-13 loss.
Del Rio declined to say who would start if Mathis can't play. Del Rio says his injury "doesn't look like it will be great for the next week or two."
Mathis underwent tests Monday to determine the severity of his injury.