using select statement

i need a solution for my simple question

is it possible to use stored procedure with output parameter in select query?

i am having stored proc "a_proc @input, @output"

 i need to get the output parameter in the select statement of the other stored proc

here's my example

declare @OP as datetime

select

a,b,c,

(exec a_proc tablex.Data1,@OP output) as [MY field name],

d,e,f

from tablex

where 'conditions'

but its here giving error .. how to use this stored procedure which returning me a variable and i need assign that O/P value to the fields in the select statement

pls its urgent!!

Thanks in advance