MySQL help please?

[Ntenze]

Here is the error.

Invalid SQL: SELECT COUNT(*) AS referrals, user.username, user.userid FROM user AS users 
                   LEFT JOIN user AS user ON (users.referrerid = user.userid) 
                   WHERE user.userid > 0
                   GROUP BY users.referrerid 
                   ORDER BY referrals DESC 
                   LIMIT 10
mysql error: Unknown column 'user.username' in 'field list'

mysql error number: 1054

Thank's for any help