Crossword Genius

Man losing energy for a darling, we hear: is he in a rut? (6,4)

Ross

I believe the answer is:

fallow deer

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

'man' is the definition.
The definition and answer can be both animals as well as being singular nouns.
Maybe there's a link between them I don't understand?

'losing energy for a darling we hear is he in a rut?' is the wordplay.
I cannot really see how this works, but
'energy' could be 'e' (physics symbol as in E=mc2) and 'e' is found within the answer.
'a' is present in the answer.
'he' could be 'der' and 'der' is present in the remaining letters.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for fallow deer that I've seen before include "Antlered animal whose summer coat is reddish with white spots" , "horny beast" , "Antlered beast" , "Wildlife" .)

I've seen this clue in The Guardian.
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