Doctor about to get further (4)
I believe the answer is:
more
'further' is the definition.
(synonyms)
'doctor about' is the wordplay.
'doctor' becomes 'mo' (medical officer).
'about' becomes 're' ('re' means regarding or about).
'mo'+'re'='MORE'
'to get' is the link.
(Other definitions for more that I've seen before include "A greater amount" , "Additional or larger amount" , "To a greater extent" , "What Oliver wanted" , "Extra (for Sir Thomas?)" .)