Mother recruited top doctor, ready for a monkey (8)
I believe the answer is:
marmoset
'monkey' is the definition.
(marmoset is a kind of monkey)
'mother recruited top doctor ready' is the wordplay.
'mother' becomes 'ma' (ma can mean mother).
'top' suggests taking the first letters (in a down clue, the first letter is top).
'doctor' becomes 'mo' (medical officer).
'ready' becomes 'set' (set can mean ready or prepared).
The initial letter of 'recruited' is 'r'.
'ma'+'r'+'mo'+'set'='MARMOSET'
'for a' acts as a link.
(Other definitions for marmoset that I've seen before include "Star memo about kind of monkey" , "Small tropical American monkey" , "Small New World monkey" , "Monkey with claws" , "Small bushy-tailed monkey" .)