Depends where you sit I think.
City V Celtic games a bit more volatile because City have a small number of orange supporters. There was trouble at a pre-season friendly a few years ago.
Every Champions League game I have been to, its been really noticeable the number of away fans sat in the home end. There were hundreds of German fans scattered in the home ends and 100s of Barcelona fans (even though they didn't fill a very small visiting allocation) in our end, but no trouble at all. More antagonism with Celtic though. It wouldn't surprise me if there's the odd incident. However game maybe a dead-rubber by then which will take some heat out of it.