isn't the basic issue that he has a lot of swelling on his knee, so they can't get a definitive MRI?
I think some hairline fractures can be obscured on imaging when there is swelling. Primarily, though, doesn't swelling preclude detection of tendon/meniscus tears? I guess what I'm saying is that as far as they are reporting, he could have a badly bruised or sprained knee (hopefully), or he could have a hairline fracture (suck), or he could need his ACL surgically repaired (massive suck).
PS - as you might be able to tell, I only play a doctor on TV.