Although the clubs play the salaries, typically national Team requests take precedence in the pecking order for call ups. Not the clubs. The players can always say they don't what to play in this or that, but that's when they "fall out of favor".thats the thing...its still up in the air which star players will come or if the best teams will be called up.
neymar has said he wants to play in olympics, i dont think barcelona lets him play two tournaments.
james has alluded to the same although that depends on wether they beat the USA.
chicharito/ tecatito/ layun/ and i think talavera have all expressed their desire to play in the olympics
sanchez may be held back by arsenal for "rest" be wenger, plus read a while back chile and ecuador were thinking of taking reserve/ U-23 teams
so if it ends up being a reserve/ not all starters being there then it becomes a meh tournament.