Doctor near poorly person who grumbles (6)
I believe the answer is:
moaner
'person who grumbles' is the definition.
(I know that moaners grumble)
'doctor near poorly' is the wordplay.
'doctor' becomes 'mo' (medical officer).
'poorly' indicates an anagram (a poor spelling).
'near' anagrammed gives 'aner'.
'mo'+'aner'='MOANER'
(Other definitions for moaner that I've seen before include "Complainer" , "Grouch" , "Grumbler" , "One who complains" .)