To deliver it to clinician at work isn't on (7)

I believe the answer is:

dropoff

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'clinician at work isn't on' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'to deliver it' is the wordplay.
'to deliver' becomes 'drop' (dropping is a kind of delivering).
'it' becomes 'off' (I can't explain this - if you can you should believe this answer much more).
'drop'+'off'='DROPOFF'

'to' acts as a link.

Can you help me to learn more?

(Other definitions for dropoff that I've seen before include "fall asleep" , "In decline" .)

I've seen this clue in The Irish Times.

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