Maybe you will not be ready in time for this ride. It's not worth it to hurt yourself permanently just so you can reach a goal set by someone else.
Knees are fragile creatures and need to be taken care of. healing takes time. a 100 mile ride with hills (or a 60 mile ride with hills) might not be what your knee should be exposed to until it is ready . there's always next year.
Lance Armstrong isn't riding this week, he's hurt. So are you.