diff -Naur wordpress/wp-includes/comment-template.php wordpress/wp-includes/comment-template.php
--- wordpress/wp-includes/comment-template.php	2018-11-19 10:30:13.901443000 +0530
+++ wordpress/wp-includes/comment-template.php	2018-11-19 10:32:40.644998494 +0530
@@ -2240,7 +2240,7 @@
 		/** This filter is documented in wp-includes/link-template.php */
 		'must_log_in'          => '<p class="must-log-in">' . sprintf(
 		                              /* translators: %s: login URL */
-		                              __( 'You must be <a href="%s">logged in</a> to post a comment.' ),
+		                              __( 'You must be <a rel="nofollow" href="%s">logged in</a> to post a comment.' ),
 		                              wp_login_url( apply_filters( 'the_permalink', get_permalink( $post_id ), $post_id ) )
 		                          ) . '</p>',
 		/** This filter is documented in wp-includes/link-template.php */