As Jason Garrison pointed out on Wednesday, there's no known time table for Keith Rivers' return after surgery that was described as "rebuilding of the wrist" when he showed up to camp in a cast.
Rivers was placed on the Non-Football Injured list (which is no-different than the Physically Unable to Perform list in terms of football rules not related to salary) and the Bengals will have to make a decision within a few weeks as to whether to activate him, release him outright or place him on Injured Reserve. Some estimates have Rivers returning as late as early December. So obviously Rivers isn't practicing on Wednesday.
Also out on Wednesday is linebacker Thomas Howard, who is working out on the side with a hamstring injury and Rey Maualuga, who is shooting for a return from an injured ankle next week against the Tennessee Titans. If none are able to go, the likely starting lineup during a base 4-3 formation would be Dan Skuta at middle linebacker with Brandon Johnson replacing Howard at the Will.