Steelers tight end David Johnson left in the first quarter of the first preseason game against the Eagles on Thursday night, and according to head coach Mike Tomlin, he could be out for a considerable amount of time. Johnson suffered a knee injury that Tomlin would characterize as "severe" after the game. Via Mark Kaboly of the Pittsburgh Tribune-Review:

Tomlin: DJ severe knee injury. Adams less significant. Dwyer AC sprain. — Mark Kaboly (@MarkKaboly_Trib) August 10, 2012

While the Mike Adams and Jonathan Dwyer injuries create less cause for concern, it does appear that Johnson could be lost for a significant portion, it not all, of the upcoming 2012 season.

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