Poet's lower than 'the man sadly emasculated' (5)
I believe the answer is:
neath
'poet's lower than' is the definition.
(archaic or poetic version of 'underneath')
'man sadly emasculated' is the wordplay.
'man' becomes 'N' (knight, a man in chess).
'sadly emasculated' becomes 'eath' (I can't justify this - if you can you should give a lot more credence to this answer).
'n'+'eath'='NEATH'
'the' acts as a link.
(Other definitions for neath that I've seen before include "town in South Wales" , "Under, poetically" , "Welsh industrial town" , "River" , "Welsh team" .)