Little monkey could do most damage round the back (8)
I believe the answer is:
marmoset
'little monkey' is the definition.
(I've seen this before)
'do most damage round the back' is the wordplay.
I cannot really understand how this works, but
'do' could be 'set' (synonyms) and 'set' is found within the answer.
'damage' could be 'mar' (to mar is to spoil or damage) and 'mar' is present in the answer.
'round' could be 'o' (o is a circular letter) and 'o' is located in the answer.
A single letter 'm' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
'could' is the link.
Can you help me to learn more?
(Other definitions for marmoset that I've seen before include "rather small creature" , "Turn morse mat over for the monkey" , "Monkey with claws" , "Take me to arms about bushy-tailed monkey of tropical America" , "Small tropical American monkey" .)