Dynamically Create Theme Location for Menu

I’m trying to dynamically add a theme location for a custom menu and I’d like to do that each time I create a new post under a custom post type. The idea is that each custom post type could have a custom menu. There will only be a few posts under that custom post type.

Here is what I have added to the functions file, but it doesn’t seem to work. Any suggestions or issues that can be easily seen?

function add_registered_menu($post_id) {
	$slug = 'players';
	// If this isn't a 'players' post, don't update it.
    if ( $slug != $_POST['post_type'] ) {
        return;
    }
    if ( wp_is_post_revision( $post_id ) )
		return;
		$menu_loc_name = get_the_title($post_id);
		$menu_loc = basename(get_permalink($post_id));
		register_nav_menu($menu_loc, $menu_loc_name);
}
add_action ('save_post', 'add_registered_menu');