Deal leads to doctor being held in row (6)
I believe the answer is:
timber
'deal' is the definition.
(I've seen this before)
'doctor being held in row' is the wordplay.
'doctor' becomes 'MB' (Bachelor of Medicine, Medicinae Baccalaureus).
'being held in' indicates putting letters inside.
'row' becomes 'tier' (a tier is a row of things).
'mb' inserted into 'tier' is 'TIMBER'.
'leads to' is the link.
(Other definitions for timber that I've seen before include "22 [BEAM]" , "Trees suitable for building or carpentry" , "Wood for building, etc" , "Wood prepared for use in carpentry or building" , "wooden" .)