You previously turned back, abandoning obsequious servant in need (4)
I believe the answer is:
lack
'need' is the definition.
(to lack something is to be in need of it)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for lack that I've seen before include "Be wanting or without" , "Be without or short of" , "Absence, deficiency" , "Deficiency or want" , "Be without, need" .)