Poorly person at home, OK? (7)
I believe the answer is:
invalid
'poorly person' is the definition.
(an invalid is poorly or unwell)
'home ok?' is the wordplay.
'home' becomes 'in' ('he's home' can mean 'he's in').
'ok?' becomes 'valid' (I can't justify this - if you can you should believe this answer much more).
'in'+'valid'='INVALID'
'at' acts as a link.
Can you help me to learn more?
(Other definitions for invalid that I've seen before include "Person disabled by injury or sickness" , "Permanently sick person" , "Nullified" , "lacking legal authority" , "Not legally binding" .)