Nobody is going to blow up Nole, nobody did in 2008 and nobody is going to do now, I'm sure most of Albanians/Kosovars couldn't care less what Serbians think.
As for the good doctor, I don't see what he could do, he fixed Nole's allergies/stamina problems, but injuries are something else, you don't fix those with a different diet. Besides, Fed is also skipping these tournaments, and he didn't even play after USO where he looked fine/no injury at all
So you think the only real harm they could do, but won't, is to blow up Djokovic?
Isn't that terribly naive?
Terrorists understand that the mere threat of their intentions is enough to mess you up completely. Just look at the US spending billions of dollars (that it really can't afford now) on security every year and inconveniencing its air travellers to laughable degrees, and you'll see how easy it is to cow the world's sole superpower, never mind a mere individual.
Do you think Nole, faced with threats against his own life - or those of his girlfriend, family, Pierre, etc. - would sail through his matches or his off-court activities unaffected by it all? Again, think back to Wimby '08.
Let's bear in mind how mental a game tennis ultimately is.
As for Cetojevic, that guy was clearly the rainmaker on Team Novak. Without him, this year wouldn't have happened. When I saw Nadal completely run out of steam in the fourth set after giving his all in the third, I was stunned beyond words. A gluten-free Nole has turned the Bull into essentially a best-of-three-sets player.
Cetojevic, I believe, would have strongly advised against Cincy and DC.