arrays - PHP 5.3.10 vs PHP 5.5.3 syntax error unexpected '['

Is it possible that this PHP code line

if ($this->greatestId()["num_rows"] > 0)

works in PHP 5.5 and returns an error in 5.3??

PHP Parse error:  syntax error, unexpected '[' in /var/www/app/AppDAO.php on line 43

How can I change it to work under PHP 5.3?