Don't expect him to work well! (5)
I believe the answer is:
scamp
'don't expect him to work well' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'him to work well' is the wordplay.
I cannot quite see how this works, but
'him' could be 'cam' and 'cam' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for scamp that I've seen before include "Mischievous child (colloq.)" , "Tearaway" , "little monkey" , "Mischief-maker" , "Rogue - perform inadequately" .)