Boss, he's considered something of a Casanova (4)
I believe the answer is:
stud
'a casanova' is the definition.
'boss he's considered something' is the wordplay.
I cannot really see how this works, but
'he' could be 'stu' and 'stu' is found within the answer.
A single letter 'd' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'of' is the link.
Can you help me to learn more?
(Other definitions for stud that I've seen before include "Sex god" , "Press to secure this" , "Breeding stable" , "kind of farm" , "Ornamental protuberance" .)