Publicist with gift for concealing decline (5,5)
I believe the answer is:
press agent
'publicist' is the definition.
(press agent is a kind of publicist)
'gift for concealing decline' is the wordplay.
'gift' becomes 'present' (present is a kind of gift).
'for concealing' indicates putting letters inside.
'decline' becomes 'sag' (I've seen this in other clues).
'present' placed around 'sag' is 'PRESS-AGENT'.
'with' is the link.
(Other definitions for press agent that I've seen before include "publicist" , "Person seeking favourable publicity on behalf a client" , "PR person" , "PA" .)