He shouldn't lie about it and shouldn't brag about it either. I realise we're being unreasonable.
1. Its obvious to everyone that hes incredibly good at the game - therefore saying that hes going to win isn't bragging, its most likely true.
2. Injecting a bit of modesty isn't lying, its trying to counter any claims of being arrogant.
3. HE IS WORLD NO.1. He has to comment. Press perpetuate interest in the game - without comments from people like him, tennis would become even more insular than it already is.
4. Yes, you are
But thats my opinion, and you have yours, which I respect, but disagree with.