Actually he knew nothing of the attack, but guessed it would end if all the eyes closed. Read that again, Danzo told him about it because sasuke acted as if he knew. And in the very first box, guess who told Sasuke of the technique. He did not know anything of the technique nor how it worked at all. Danzo said you know about this, then Sasuke said, I do now. I do not understand how people say they read the manga, put up the quotes, and still are unable to read and understand them. If he knew, he would not said well i do now. Please use logic when making an arguement, not just opinion or love for a character. Danzo wasn't really worried about Sasuke the whole fight anyways, most of the manga of that fight, he was worried about getting Tobi, Sasuke was nothing to him, which was his downfall.
If he would have actually worried just about Sasuke, he would have won, with trouble ofcourse. And Danzo is on the lower end of the spectrum of kages, Kakashi was more powerful the Danzo, he just was able to use the village being destroyed to his advantage. As I have said, Sasuke is not weak, he is just stupid at this point. If he would actually use his techniques like he did in the first part of the series, he would be top 5 no questions asked. Sasuke's weakness is he does not think of what he does at this point, he just puts our his techniques and hopes they win. And as we saw at the Kage summit, that doesn't work with high level ninjas.