Doctor had to be overwhelmed (7)
I believe the answer is:
drowned
'overwhelmed' is the definition.
('drown' can be a synonym of 'overwhelm')
'doctor had' is the wordplay.
'doctor' becomes 'dr' ('Dr' can be a synonym of 'doctor').
'had' becomes 'owned' ('own' can be a synonym of 'have').
'dr'+'owned'='DROWNED'
'to be' acts as a link.
(Other definitions for drowned that I've seen before include "Lost at sea" , "Died underwater" , "Died by submersion" , "Submerged, flooded" , "Suffocated in water" .)