Suffering understudy before gala opening (8)

I believe the answer is:

standing

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'suffering' is the definition.
('stand' can be a synonym of 'suffer')

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for standing that I've seen before include "(Of corn) not yet reaped" , "Being a candidate - status" , "Social reputation" , "Buying a round on one's feet" , "Good repute" .)

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

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