From VG247:

Assassin’s Creed II’s chances will not be hampered by the near-identical release date of Modern Warfare 2, creative director Patrice Desilets told VG247 at GamesCom, thanks to its difference in nature.

Did you know the original Assassin’s Creed went head-to-head with Modern Warfare in 2007 and sold 9 million units? We didn’t.

“The first game we released two weeks after Modern Warfare, and we still sold 9 million copies,” said the developer.

People, when they want their first-person shooter fix, they buy Modern Warfare. If you want you a swords, running on rooftops, big open city fix, this is it.

And there are people that want to play that, and they don’t want to play the game with guns.

We don’t think it’s that cut and dry, but the two games will have some overlap, and it s up to each game’s marketing to highlight the strengths of their product.  Our money is on Modern Warfare 2 pulling it out, but Assassin’s Creed II will be right on its tail.