Now, before I start, I'll be fair and say that maybe Nadal really is having a knee problem that he suffered from silently for months only to expose a day or two after losing at the French Open and thus tainting Soderling's victory. If that's the case I owe him an apology.
But it should be noted that he might be less likely to be drug tested if he skips this tournament. Anyway, you have to admit that his whining about drug testing, coinciding with his losing 2 on clay and a claim of an injury that puts him out of a tournament where he would likely be drug tested has to at least make for the possibility that he is dropping out of it to avoid drug testing.
Update: I'm not sure if I pointed this out, but the only two out-of-competition drug tests that Nadal received last year were urine only. NO OUT OF COMPETITION BLOOD TESTS WERE PERFORMED on any player last year. We have not been told whether anyone tested positive for anything the entire year. We have not been told if anyone missed an out of competition test. We have not been told to what extent these out of competition urine tests were observed or whether the player just went into the bathroom and came out with a cup of urine.