Doctor in rush, working (7)
I believe the answer is:
surgeon
'doctor' is the definition.
(surgeon is a type of doctor)
'rush working' is the wordplay.
'rush' becomes 'surge' (synonyms).
'working' becomes 'on' (e.g. a machine is working or on).
'surge'+'on'='SURGEON'
'in' is the link.
(Other definitions for surgeon that I've seen before include "Doctor in operating theatre - RN doctor" , "Physician" , "One who operates" , "incisive person" , "Medical operator" .)