It depends, really. Generally on a non-contact injury like that the tissue in the knee isn't hurt.
One of my buddies was going up for a lay in once and was run into by a guy who was trying to block it. He landed directly on the side of the knee and tore his ACL as well as popped the kneecap...
This picture shows it pretty well:
http://media.oregonlive.com/behindblazersbeat/photo/greg-odenjpg-b860a6ea32e477ae.jpg
As you can see, the kneecap is off to the side, which is why I thought/was hoping that it was just a dislocated kneecap. The knee is "twisted' simply because he moved it...
Sure if he had torn his ACL or patellar tendon, for instance, that probably would have been the worst possible thing (other than a crazy Shaun Livingston style "blow the entire knee up" thing). But a dislocated patella and he would have been back in a couple months.
The best possible news would have been a dislocated kneecap (which is what I thought it was at the time). Fractured kneecap is one of the worst possible diagnoses.
Nate's partially correct in that it is up to the players to figure out how to play well with each other. With more time playing together they will eventually strike a balance between Roy, LMA, and Oden. The success of these three playing well together at a high level is the key to Portland...
Considering I'm going to start camping out for tickets at Reser on Friday night -- if Oregon State ends up losing I'm going to send an invoice to Chip demanding I get a refund for having all that time wasted due to his team winning.