Drupal 7 edd rel="nofollow" to menu links More about: https://api.drupal.org/api/drupal/includes%21menu.inc/function/theme_menu_link/7

menu_link_nfollow.php

<?php
// Add rel="nofollow" to menu.
function themename_menu_link__menu_name(&$vars) {
  $element = $vars['element'];
  $subs_menu = '';

  // Add links for nofollow attribute add by menu link ID.
  $include_id = array();

  if ($element['#below']) {
    $subs_menu = drupal_render($element['#below']);
  }

  if (in_array($element['#original_link']['mlid'], $include_id)) {
    $element['#localized_options']['attributes']['rel'] = 'nofollow';
  }
  else {
    $element['#localized_options']['attributes']['rel'] = '';
  }

  $output = l($element['#title'], $element['#href'], $element['#localized_options']);
  return '<li' . drupal_attributes($element['#attributes']) . '>' . $output . $subs_menu . "</li>\n";
}
?>