You must use a temporary table and an alias:
SELECT SQL_CALC_FOUND_ROWS *
FROM meruca_posts
WHERE ID NOT IN (SELECT ID
FROM (
SELECT object_id as ID
FROM meruca_term_relationships
WHERE term_taxonomy_id IN (14)
)
AS temp_object)
AND post_type="post"
AND post_status IN ('publish','private')
GROUP BY ID ORDER BY post_date DESC LIMIT 0, 10