One-man medical circle in the District of Columbia! (3)

I believe the answer is:

doc

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'one-man medical' is the definition.
'doc' can be an answer for 'medical' (thesaurus). I am not sure about the 'one-man' bit.

'circle in the district of columbia' is the wordplay.
'circle' becomes 'O' (O is a circle).
'in the' indicates putting letters inside.
'district of columbia' becomes 'DC' (synonyms).
'o' going inside 'dc' is 'DOC'.

Can you help me to learn more?

(Other definitions for doc that I've seen before include "Quack" , "Main dish" , "Fox perhaps" , "One of the seven dwarfs" , "Medic (colloq.)" .)

I've seen this clue in the Evening Standard.

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