What am I doing wrong here? WordPress database error

I'm just trying to insert values into custom table of wordpress and it throws me this error

WordPress database error: 
[You have an error in your SQL syntax; 
check the manual that corresponds to your MySQL server version for the right syntax to use near 
'( post_id, site_id, u_id, is_present ) 
VALUES ( 989, 139, '1' at line 2]
INSERT INTO ( post_id, site_id, u_id, is_present ) VALUES ( 989, 139, '10822456', 'false' )

I'm using prepare query to Protect Queries Against SQL Injection Attacks.

Here is my code

$wpdb->query($wpdb->prepare(
"
    INSERT INTO $wpdb->wp_plugs
    ( post_id, site_id, u_id, is_present )
    VALUES ( %d, %d, %d, %s )
",
    $post_id,
    $site->ID,
    $u_id,
    'false'
) );