Geordie wrestler cutting head, in pain, developed illness (9)
I believe the answer is:
pneumonia
'illness' is the definition.
(pneumonia is a kind of health problem)
'geordie wrestler cutting head in pain developed' is the wordplay.
I cannot really see how this works, but
'geordie' could be 'ne' (Geordies are from Tyneside in the North East) and 'ne' is present in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for pneumonia that I've seen before include "Inflammation of the lungs" , "ailment" , "Piano menu? (anag)" , "Respiratory disease" , "complaint" .)