Disease of beef (9)
I believe the answer is:
complaint
This clue is a double definition.
'disease' is the first definition.
(medical complaint)
'beef' is the second definition.
(I know that beef can be written as complaint)
'of' acts as a link.
(Other definitions for complaint that I've seen before include "A disease" , "Protest" , "ill-feeling" , "Objection" , "cause for an expression of disappointment" .)