From the Clippers' press release:
I'm not a doctor, but I'm pretty sure that's not good.
In laymen's terms, his knee exploded. The three main structures holding the knee together are torn. Of the four main ligaments in the knee, only the lateral collateral ligament (LCL) was spared. ACL, PCL and MCL - that's the trifecta my friends. To put it into perspective, a tear to any one of those ligaments is career-threatening. He tore all three. I've literally never heard of such a thing.