Wow - that's a lot more than just bark damage. Whatever "injury" occurred went a lot deeper. Do you know how that happened? Because even common canker wouldn't cause that sort of damage. Looks like something from an outside source. Do you employ a landscaping/maintenance company? I hate to be the bearer of bad news, but I doubt you'll be able to save the tree if it's already showing unthriftiness because of this.
My body is a temple. Unfortunately, it's a fixer-upper.