In reply to alx:
As Putin has been "bigged up" on all his so-called "hard man" photo opportunities, I wouldn't be surprised if he's really completely incapable of fighting back - at least not unless his opponent is tied to a chair.
Real reasons he's not going;
1) He's scared of being shown to be a "powder-puff".
2) Someone will organise a coup while he's gone.
3) Someone (on his own side) will assassinate him once he leaves the safety of the Kremlin.
4) A combination of all 3 above.