Affected person regrets surgery going the wrong way (6)
I believe the answer is:
poseur
'affected person' is the definition.
(I've seen this before)
'regrets surgery going the wrong way' is the wordplay.
'regrets' becomes 'rues' ('rue' can be a synonym of 'regret').
'surgery' becomes 'op' (short for operation).
'going the wrong way' shows that the letters should be reversed in order.
'rues'+'op'='ruesop'
'ruesop' written backwards gives 'POSEUR'.
(Other definitions for poseur that I've seen before include "Person who's affected" , "Pretentious type" , "Attitudiniser (Fr.)" , "One shows off to impress" , "Affected type" .)