Ravi, I think the experts (not me) can help you better with this if you can explain the product you're using (server/ desktop), how & where you are publishing the report to, & its authentication protocols.
Ravi, how are you. Did the experts help you ? bechause I have the same need.
How did you do it?
It's a little hard to say without an example workbook or data structure but I'll make a couple assumptions.
First, your columns are defined as individual fields and not an attribute of 1 specific field pivoted out.
If this is the case then you could create a calculated field for you your manager dimension that looks something like the following:
if ISMEMBEROF('Managers') then [Manager] else "" end
"Managers" would be the group name that you have determined that would be allowed to see the manager field.
This will leave a blank space where the manager field is if the person that is logged in is not in that group.
Another approach would be to restructure your data so that you have a record for each dimension attribute for an employee as a single record and then you could apply row level filtering based off of the user groups.
Like I said I don't know enough about your scenario to know if these approaches are usable.
Adding to Aaron's reply adding few threads & articles -
But for column level security you can vote in idea section - http://community.tableau.com/ideas/3274