Following a 22-20 overtime loss to Miami, coach Marvin Lewis said his medical staff believed the injury was serious.
''They think he has an ACL injury,'' Lewis said. ''We won't know until we get home.''
Atkins, who made the Pro Bowl each of the past two seasons, was hurt in the second quarter and walked off the field with assistance from two teammates. He came into the game with a team-high five sacks and added another in the first quarter.
He was on crutches after the game.
''It stinks because he's one of the best,'' defensive tackle Domata Peko said. ''We'll keep him in our prayers, and Bengals Nation, please keep him in your prayers also.''
Second-year pro Brandon Thompson replaced Atkins.
''Right now we're kind of thin,'' Thompson said, ''but we just have to do what we have to do to make it. It's next man up, got to keep it ticking. I've been prepared and now it's my time to step up.''
The Bengals were already without Pro Bowl left tackle Andrew Whitworth, middle linebacker Rey Maualuga, safety Taylor Mays and backup linebacker Michael Boley, who were hurt last week.
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