Johnson (knee) is doubtful to return to Thursday's preseason contest against the Seahawks, Larry Mayer of the Bears' official site reports.
Johnson appeared to suffer a knee injury defending a running play during Thursday's contest. The linebacker managed to walk to the locker room with only a slight limp, but there's not yet an indication of how long he'll remain sidelined. Johnson filled a key role on the Bears' special-teams units last season, so the team will be searching for a replacement should his absence linger.