As part of the army, about to tear ligament (10)

I believe the answer is:

regimental

'as part of the army' is the definition.
(a regiment is part of an army)

'about to tear ligament' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'to tear' indicates anagramming the letters.
'ligament' is an anagram of 'gimental'.
're'+'gimental'='REGIMENTAL'

(Another definition for regimental that I've seen is " Of a large army unit".)

I've seen this clue in The Guardian.

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