A German undermined boss (7)

I believe the answer is:

manager

I'm a little stuck... Click here to teach me more about this clue!

'boss' is the definition.
(I know that manager is a type of leader of organization)

'a german undermined' is the wordplay.
'a german' anagrams to 'MANAGER'.
However, I am unsure how this is indicated.

Can you help me to learn more?

(Other definitions for manager that I've seen before include "Organiser" , "Sports team controller" , "Person in charge of staff" , "Ran game (anag.)" , "head of department" .)

I've seen this clue in The Mirror.

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