If it's an ulcer type wound, or open at all, or even an abrasion, it should be treated. Remove the fish and quarantine it, and put salt in the water. Someone here will give the correct ammount of salt. Be sure there is aeration, and keep the water clean. You can also buy medicated food, that helps fight infection.
I treated a fish successfully this way last year. One interesting thing - while he was quarantined in salted water, he faded and changed color. He went to a new home after he was healed up, so I don't know if his original color came back.
This year I had fish with little bumps, one per fish, not open sores and not tiny like ich, but under the skin, pushing the scales up. On both fish, the bumps eventually went away.
I've lost three fantails in the last few weeks, and one just this morning. Maybe it IS the change in the weather.