Low singer in club assessed (4)
I believe the answer is:
bass
'low singer' is the definition.
(I've seen this before)
'in club assessed' is the wordplay.
'in' indicates a hidden word.
'BASS' is hidden within 'club assessed'.
(Other definitions for bass that I've seen before include "Freshwater fish and lowest voice" , "Scottish rock" , "Fish; vocalist" , "A fish, or the lowest pitch in music" , "Fish, guitar" .)