Index: src/wp-admin/menu-header.php
===================================================================
--- src/wp-admin/menu-header.php	(revision 33902)
+++ src/wp-admin/menu-header.php	(working copy)
@@ -36,6 +36,16 @@
  */
 $parent_file = apply_filters( 'parent_file', $parent_file );
 
+/**
+ * Filter the file of an admin menu sub-menu item.
+ *
+ * @since 4.4.0
+ *
+ * @param string $submenu_file The submenu file.
+ * @param string $parent_file  The submenu item's parent file.
+ */
+$submenu_file = apply_filters( 'submenu_file', $submenu_file, $parent_file );
+
 get_admin_page_parent();
 
 /**