Joseph is in the locker room and being evaluated for a head injury after leaving Friday's preseason game against the Seahawks, Rob Phillips of the Cowboys' official site reports.
Joseph collided with an offensive player following an incompletion on the first drive of the game, but the extent of the injury remains unclear. The second-year cornerback appeared in 10 games as a rookie, recording 16 tackles and two pass defenses, and he's vying for an increased role in Year 2.