If he reinjures a knee that he injured at Inter and can not play for 6 months than Real can send him back to Inter and Inter have to give back the money they recieved for Ronaldo. Win-win situation for Real I think.
I'd love to see the details of this deal. What if R9's knee is injured with a collision with someone else? Does that 'count'? My point is it will be very difficult to prove that a new injury was or was not related to previous ones.