No surgery date has been announced.
The six-year veteran, Chicago's strong-side linebacker, was injured in the first half of last Sunday's 21-14 loss to the Falcons at Atlanta.
His game totals were four tackles with one forced fumble.
"Whenever you have a player like Pisa go down, (it hurts)," Head Coach Lovie Smith told the Chicago Sun Times earlier this week. "Hopefully we can get Hunter (Hillenmeyer) to fill back in, so our numbers are still pretty good."
Hillenmeyer has been on the injured list the last three weeks with two fractured ribs, but is expected to start Sunday at Cincinnati.
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