Agent at unit being treated is getting weaker (11)

I believe the answer is:

attenuating

'getting weaker' is the definition.
(attenuating is a kind of getting weaker)

'agent at unit being treated' is the wordplay.
'being treated' indicates an anagram.
'agent'+'at'+'unit'='agentatunit'
'agentatunit' with letters rearranged gives 'ATTENUATING'.

'is' acts as a link.

I've seen this clue in The Telegraph.

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