Debugger to a non-debuggable Android app

I want to know can we attach a debugger to an app running on the smartphone which is published over Google Play Store ***without modifying the original app***? The reasons for asking this is by default the app which is there over Google playstore are non debuggable, i.e in the AndroidManifest.xml file, either they won't have android:debuggable flag or if it is, then it will be set to **false**