Vehicle doctor has to use again losing energy once (10)
I believe the answer is:
motorcycle
'vehicle' is the definition.
(motorcycle is a kind of vehicle)
'doctor has to use again losing energy once' is the wordplay.
I cannot really see how this works, but
'doctor' could be 'mo' (medical officer) and 'mo' is found in the answer.
'to' is found in the answer.
'energy' could be 'e' (physics symbol as in E=mc2) and 'e' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for motorcycle that I've seen before include "Triumph for rider, perhaps" , "Two-wheeled vehicle" , "It's used for scrambling" , "Petrol-driven two-wheeler" , "transport" .)