Swimmer suffered cut (7)
I believe the answer is:
haddock
'swimmer' is the definition.
(haddock is a kind of fish)
'suffered cut' is the wordplay.
'suffered' becomes 'had' ('have' can be a synonym of 'suffer').
'cut' becomes 'dock' (docking is a kind of cutting).
'had'+'dock'='HADDOCK'
(Other definitions for haddock that I've seen before include "Fish like cod but smaller" , "Popular food fish" , "ish" , "N. Atlantic food fish" , "Swimmer" .)