Assigned setter is placed by news boss (7)
I believe the answer is:
imputed
'assigned' is the definition.
('impute' can be a synonym of 'assign')
'setter is placed by news boss' is the wordplay.
'setter is' becomes 'im' (the setter is the person who set the crossword).
'placed' becomes 'put' (I've seen this in other clues).
'by' says to put letters next to each other.
'news boss' becomes 'ed' (I've seen this in other clues).
'im'+'put'+'ed'='IMPUTED'
(Other definitions for imputed that I've seen before include "Attributed (something bad to someone)" , "Attributed or ascribed, say a fault" .)