Medic neutered them accidentally but isn't discouraged (10)
I believe the answer is:
undeterred
'medic neutered them accidentally' is the definition.
I can't judge whether this definition defines the answer.
'isn't discouraged' is the wordplay.
'isn't' becomes 'un' (I can't justify this - if you can you should believe this answer much more).
'discouraged' becomes 'deterred' ('deter' can be a synonym of 'discourage').
'un'+'deterred'='UNDETERRED'
'but' is the link.
Can you help me to learn more?
(Other definitions for undeterred that I've seen before include "Nothing daunted" , "Not put off" , "Ignoring danger" , "going on regardless" , "without hindrance" .)