Johnson, listed first on the depth chart at his position, was injured on a running play Tuesday. He dropped immediately to ground and rolled over on his back before medical personnel arrived within 1 minute.
The Falcons and Cincinnati Bengals were practicing together for the second straight day.
Both teams will be missing some starters when Atlanta hosts Cincinnati in Thursday's preseason opener.
Falcons receiver Julio Jones has sore hamstrings and linebacker Sean Weatherspoon is sidelined indefinitely with a dislocated left finger that resulted in an open wound.
Receiver A.J. Green has a bruised knee and left tackle Andre Whitworth a sore knee for Cincinnati.
http://accesswdun.com/article/2013/8/264254