Operator performing under sudden influx (7)
I believe the answer is:
surgeon
'operator' is the definition.
(thesaurus)
'performing under sudden influx' is the wordplay.
'performing' becomes 'on' (I've seen this in other clues).
'under' means one lot of letters go next to another.
'sudden influx' becomes 'surge' (I've seen this before).
'on' put after 'surge' is 'SURGEON'.
(Other definitions for surgeon that I've seen before include "incisive person" , "Physician" , "Naval doctor" , "Doctor in operating theatre - RN doctor" , "Medical operator" .)