Found a way… instead of using wp_nav_menu()
$menu_name="main-menu";
if ( ( $locations = get_nav_menu_locations() ) && isset( $locations[ $menu_name ] ) ) {
$menu = wp_get_nav_menu_object( $locations[ $menu_name ] );
$menu_items = wp_get_nav_menu_items($menu->term_id);
$menu_list="<ul id="menu-main-menu">";
foreach ( (array) $menu_items as $key => $menu_item ) {
$title = $menu_item->title;
$url = $menu_item->url;
$id = $menu_item->ID;
$menu_list .= '<li id="menu-item-' . $id . '"><a href="' . $url . '"></a><div class="pop_up">' . $title . '</div></li>';
}
$menu_list .= '</ul>';
}
echo ($menu_list);