Implant doctor in rising river (5)
I believe the answer is:
embed
'implant' is the definition.
('embed' can be a synonym of 'implant')
'doctor in rising river' is the wordplay.
'doctor' becomes 'mb' (Bachelor of Medicine, Medicinae Baccalaureus).
'in' is an insertion indicator.
'rising' shows that the letters should be reversed in order (going up in a down clue).
'river' becomes 'dee' (River Dee).
'dee' reversed gives 'eed'.
'mb' placed inside 'eed' is 'EMBED'.
(Other definitions for embed that I've seen before include "Firmly put down" , "bringing plant inside" , "Fix fast in something solid" , "Implant (eg, an idea)" , "Surround" .)