Serious complaint? (6,7)

I believe the answer is:

severe illness

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'serious complaint?' is the definition.
The definition suggests a singular noun which matches the answer.

'serious complaint?' is the wordplay.
'serious' becomes 'severe' (synonyms).
'complaint?' becomes 'illness' (illness is a kind of health problem).
'severe'+'illness'='SEVERE ILLNESS'

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I've seen this clue in The Globe and Mail.

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