Expression of relief as man found in outskirts of Warsaw (4)
I believe the answer is:
whew
'expression of relief' is the definition.
(I've seen this before)
'man found in outskirts of warsaw' is the wordplay.
'man' becomes 'he'.
'found in' means one lot of letters goes inside another.
'outskirts of' means to remove the middle letters.
'warsaw' with its centre taken out is 'ww'.
'he' put inside 'ww' is 'WHEW'.
'as' acts as a link.
(Other definitions for whew that I've seen before include "expression of surprise" , "Expression of relief" , "Bustle about" .)