Assuming he's at least at arm's length and not specifically looking for injuries: personally, I would think that he could smell the antiseptic and blood of recent-ish minor wounds and infer that someone was injured, but not with certainty, and not /exactly/ where. With stitches, he might be able to hear the way clothing catches on them (or on the bandage covering them), and that would certainly pinpoint them.

The better he knows the person, the more likely I think it would be that he could tell that something was wrong and be able to figure out the specifics a little better. With Foggy, for instance, if he had a torso injury that made deep breaths uncomfortable, Matt would certainly notice that he was breathing a bit more shallowly that usual, or he could pick up slight differences in he gait, but with someone he doesn't have a "default" for, it would be harder for him to know what was outside of their normal.