Doctor has son to encourage (7)
I believe the answer is:
surgeon
'doctor' is the definition.
(surgeon is a kind of doctor)
'son to encourage' is the wordplay.
'son' becomes 's'.
'to encourage' becomes 'urgeon' (urging on is a kind of encouraging).
's'+'urgeon'='SURGEON'
'has' is the link.
(Other definitions for surgeon that I've seen before include "Medical man" , "Theatre worker" , "Sawbones" , "Man with knife" , "Naval medic" .)