First off, talk to a Dr. and PT about this.

Other than that, thesmoothdome's experience matches my own. I broke a kneecap and the tendonitis after that lasted for years. Get in the habit of not doing anything that irritates it. I learned to pedal with my glutes a bit more and got the power back up. It's been 9 years now, and I really think this is the first year I've felt like I don't have any tendonitis.

To put it in perspective though, the last two years have been some amazing race results for me, even with the injury, including many race wins and upgrading to Cat 2 (I've since requested a downgrade because I lost a bunch of weekly training hours). The point is that it doesn't need to kill your cycling. Focus on what hurts and don't do that. Your muscles will figure out how to fire at the right times and how not to at the wrong times.

Just don't ever do anything that hurts it. I would go months and realize I hadn't "tested" my knee in a while (hadn't felt it hurt). After testing, I'd realized that it still hurt, but I could do more with it, so healing had occurred. Just be patient with it and deal with it.

Oh, and go see a Dr.