It's said to deny being feverish when unwell (3,2,3)
I believe the answer is:
not so hot
'unwell' is the definition.
Both the definition and answer are adjectives.
Maybe you can see an association between them that I can't see?
'it's said to deny being feverish' is the wordplay.
I cannot quite understand how this works, but
'it's' could be 'ts' (abbreviation. e.g. in 'tis) and 'ts' is located in the answer.
'feverish' could be 'hot' (I've seen this in another clue) and 'hot' is found in the answer.
The remaining letters 'noo' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'when' is the link.
Can you help me to learn more?