Redskins Tight End Fred Davis -- COTTON-MOUTHED MUG SHOT ... After DUI Bust

TMZ Sports has obtained Fred Davis' mug shot ... taken moments after the troubled Washington Redskins tight end was arrested for DUI in Virginia on Thursday.

Davis was arrested at 3:45 PM -- and hauled to a nearby station where he was booked and posed for an angry mug shot, in which he looks like he's dying for some water.

It's been a bad week for the 28-year-old -- on Wednesday, the NFL suspended him indefinitely for violating the league's substance abuse policy. Davis insists he was merely taking a substance that was not FDA approved.

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