It depends what the leaf looks like, do you think this is some kind of problem with the plant itself, or something made a whole in it. (Snail, person, whatever) If it is a problem with the plant itself you should cut the leaf off because it will divert energy to that leaf even if it is going to die anyway. If something chewed a whole in the leaf, leave it, it will be fine, (I don't think the hole will go away though)