Distress when a French copper cuts foot (7)
I believe the answer is:
afflict
'distress' is the definition.
(thesaurus)
'a french copper cuts foot' is the wordplay.
'french copper' becomes 'flic' (I've seen this in another clue).
'cuts' is an insertion indicator (some letters cut their way into a word).
'foot' becomes 'ft' (abbreviation).
'flic' put into 'ft' is 'fflict'.
'a'+'fflict'='AFFLICT'
'when' is the link.
(Other definitions for afflict that I've seen before include "Distress severely" , "Cause distress to" , "Ail" , "Cause pain to" , "Painfully affect" .)