The dog, if upset, needs a word of encouragement (4)
I believe the answer is:
fido
'the dog' is the definition.
(I've seen this before)
'if upset needs a word of encouragement' is the wordplay.
'upset' says the letters should be written backwards.
'needs' says to put letters next to each other.
'a word of encouragement' becomes 'do' (I can't explain this - if you can you should give a lot more credence to this answer).
'if' in reverse letter order is 'fi'.
'fi'+'do'='FIDO'
Can you help me to learn more?
(Other definitions for fido that I've seen before include "Dog perhaps" , "it would disperse fog" , "Fog disperser" , "Typical dog's name" .)