Worker was first to be manipulated (7)
I believe the answer is:
handled
'manipulated' is the definition.
(handling is a kind of manipulating)
'worker was first' is the wordplay.
'worker' becomes 'hand' (hand is a kind of worker).
'was first' becomes 'led'.
'hand'+'led'='HANDLED'
'to be' acts as a link.
(Other definitions for handled that I've seen before include "managed" , "Touched - held" , "Dealt with" , "Coped with" .)