Doctor finding new ruler in bed (10)
I believe the answer is:
consultant
'doctor' is the definition.
(I have seen 'Senior doctor' mean 'consultant' so perhaps 'doctor' could also mean 'consultant')
'new ruler in bed' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'ruler' becomes 'sultan' (sultan is a kind of ruler).
'in' is an insertion indicator.
'bed' becomes 'cot' (cot is a type of bed).
'n'+'sultan'='nsultan'
'nsultan' inserted inside 'cot' is 'CONSULTANT'.
'finding' is the link.
(Other definitions for consultant that I've seen before include "Specialist" , "Adviser" , "Senior hospital doctor" , "See 1 across" .)