Try with print render($node_author->field_custom);

Try with print render($node_author->field_custom);

Or you can try as well:

insert at the top of you node.tpl.php

<?php 
global $user;
$node_author = user_load($user->uid);
$yourvariable = $node_author->field_custom;
?>

Where you want print the field insert:

<?php print $yourvariable['und'][0]['value'];?>