YES. It just might be that your client forgets or doesn't want to bother leaving any feedback. It's a gamble, of course, but there are quite a few who don't. I agree with others who commented that asking clients NOT to leave feedback is uncool. Chances are you might be happily surprised. And you don't have to leave feedback. Yes, the system will remind you to do so, but you can always ignore that. After two weeks' time, voila! Whatever was or was not entered will post on your profile. Best advice I'd give is to rise above and, as the old poem reads, "be to his faults a little blind." There is never a time not to be courteous.
Like William said, it would be unprofessional to request that your client doesn’t provide truthful feedback. Remember that you can too, share your thoughts in a constructive manner. Suzanne and Katrina are correct, freelancers cannot hide the written feedback from clients, or vice versa. Feedback is there to provide transparency into the working relationships of past jobs.