Matthew Stafford  believes he injured his right hamstring or glut, and will have an MRI  on Monday to determine the damage. Stafford said the injury started to  bother him this past week in practice and flared up during Detroit's  44-41 overtime loss against the Tennessee Titans on Sunday.   Lions tight end Brandon Pettigrew was stripped by Tennessee's Alterraun  Verner late in the fourth quarter, and he returned it 72 yards for a  touchdown, giving Tennessee a 41-27 lead. Stafford attempted to run down  Verner, which caused the flare up.