As I'm the chosen one, I go to make complaint (8)
I believe the answer is:
Here is my best explanation:
'complaint' is the definition.
(impetigo is a kind of disease)
'as i'm the chosen one i go' is the wordplay.
I cannot really see how this works, but
'i'm' could be 'im' and 'im' is located in the answer.
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
'go' is present in the answer.
The remaining letters 'pet' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
'to make' acts as a link.
(Other definitions for impetigo that I've seen before include "I omit peg to get the childhood skin infection", "Skin infection", "unsightly condition", "Skin disease", "Contagious skin disease causing crusted spots", "complaint", "Contagious skin disease causing spots and yellow crusts", "sickness", "Complaint" and "Contagious skin disease with crusty spots".)