@variable('DBUSER') returns a value is surrounded by single quotes

Hello experts,

I am using  @Variable('DBUSER' [DELIMITER = no_quote] ) but still the return value has single quote in generated sql statement.

SELECT DISTINCT

  'MYDB'.FXN_CUSTOM_FUNCTION('08/19/2015 16:58:18')

FROM

  MYTABLE

In above example MYDB is the output of @variable('DBUSER'), it is surrounded by single quotes and hence i am getting an error saying

[Microsoft][SQL Server Native Client 11.0][SQL Server]Cannot call methods on varchar.

Can any one tell me how to get out of single quotes here.

Thanks ,

Deepa.