DETROIT — The Detroit Lions were already down several key defenders in the secondary heading into their Thursday Night Football matchup, and now they’ll be without another.

The Lions’ medical staff has downgraded safety Thomas Harper as out for the remainder of the Week 14 game against the Dallas Cowboys after he suffered a concussion in the opening quarter.

Harper was making his seventh consecutive start in place of injured All-Pro safety Kerby Joseph.

On Dallas’ opening drive, Cowboys quarterback Dak Prescott connected with receiver George Pickens on an 11-yard gain during a second-and-six play from the Cowboys’ 36-yard line. Harper was in position to make the tackle when his head collided with Pickens’ thigh.

Harper was slow to get to his feet and needed assistance from the medical

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