There isn't many players that are what I call 'bad' matchups for Novak in the same sense of Fedal, Del Potro, Berdych and others. (Perhaps players with power games who also have good slices) I mean it's clear that for example Roger and Rafa both have very specific types of players and gamestyles that they don't like to play against and seem to steamroll everything else.
Novak on the other hand doesn't really seem to have that same Achilles heels. The flip side is that his gamestyle isn't necessarily a bad matchup for the rest of the tour. It's really pretty basic aggressive control style tennis, simply executed at a very high level and I don't really think it makes most tennis players uncomfortable perse.
So perhaps more than Fedal, he is vulnerable to simply being beaten by a hot player who's in rhythm while he himself is not, even if that player perse doesn't really have a style that bothers him. So I think If DelPo has a great day, he can outright beat Novak. I just don't think its likely, considering Novaks overall level is number 1 for a reason.