Doctor, I have to be at the wheel (5)
I believe the answer is:
drive
'be at the wheel' is the definition.
'doctor i have' is the wordplay.
'doctor' becomes 'dr' ('Dr' can be a synonym of 'doctor').
'i have' becomes 'ive' (**).
'dr'+'ive'='DRIVE'
'to' is the link.
(Other definitions for drive that I've seen before include "Energy - herd - private road" , "Propel; outing" , "Motor < car storage space" , "Motivate" , "High motivation, ambition" .)