Coach Mike Smith said Thursday Spruill tore his anterior cruciate ligament late in Wednesday's practice. Spruill was on the field for several minutes before walking off with the help of trainers.
The Falcons lost starter Sean Weatherspoon to a season-ending Achilles tendon injury in June.
The depth chart was configured for a nickel defense. He likely would have been a top backup inside linebacker on a depth chart configured for a 3-4 scheme.
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