Manager retains old craftsman (6)
I believe the answer is:
cooper
'craftsman' is the definition.
(cooper is a kind of craftsman)
'manager retains old' is the wordplay.
'manager' becomes 'coper' (someone who manages or copes).
'retains' is an insertion indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'coper' placed around 'o' is 'COOPER'.
(Other definitions for cooper that I've seen before include "Cask/barrel maker" , "Maker of barrels" , "Barrel-maker" , "He makes and repairs barrels" , "Porter with stout" .)