Old soldier your pet may not like very much (3)
I believe the answer is:
vet
'old soldier' is the definition.
(I've seen this in other clues)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for vet that I've seen before include "Screen" , "Experienced" , "animal doctor to > investigate" , "Check someone for suitability" , "Animal doctor, in brief" .)