His knee will be fine. There was that star guy who had a heart condition DID NOT WANT at 14 clearly 5th rounder now.
Stars heart condition was found to not be life threatening after further testing, teams were only scared because he still had that label and there is a general stigma attached to the label heart conditions.
Kouandjio has an arthritic knee, something we know a lot more about. There's no if's but' or maybe's, at some point in his life this will seriously affect his ability to walk, especially at that weight. It's just a guess as to whether it's during his playing career (which will likely aggravate the injury) or afterwards. With a knee like that it is highly likely that he will regularly half to ice his knee during the week and miss practice regularly to be able to play on Sundays.
If he had tested well at the combine then maybe you can overlook the arthritis as it is having no affect but with his scores from yesterday it looks like his knee is already deteriorating. I wouldn't spend more than a fifth on the guy. He's still very talented but its risk reward with that injury.