Doctors, say, included what's left (5)
I believe the answer is:
dregs
'what's left' is the definition.
(I've seen this before)
'doctors say included' is the wordplay.
'doctors' becomes 'Drs' ('Dr' can be a synonym of 'doctor').
'say' becomes 'eg' (both can mean 'for example').
'included' is an insertion indicator.
'drs' enclosing 'eg' is 'DREGS'.
(Other definitions for dregs that I've seen before include "Grounds; refuse" , "Sediment at bottom of drink" , "Most worthless parts" , "Parts of least value" , "Lees - riffraff" .)