Assessed as immovably stuck, without energy (5,2)

I believe the answer is:

sized up

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'assessed' is the definition.
Although both the answer and definition are past participle verbs, I cannot see how one could define the other.

I cannot understand how the remainder of the clue works.

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(Other definitions for sized up that I've seen before include "Estimated (the) dimensions (of)" , "Used zip (anag.)" .)

I've seen this clue in the Sydney Morning Herald.

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