Old countryman sick, having broken blood vessel (7)
I believe the answer is:
villein
'old countryman' is the definition.
(historical term for agricultural worker)
'sick having broken blood vessel' is the wordplay.
'sick' becomes 'ill' (similar in meaning).
'having broken' is an insertion indicator.
'blood vessel' becomes 'vein' (vein is a kind of blood vessel).
'ill' going within 'vein' is 'VILLEIN'.
(Other definitions for villein that I've seen before include "vassal" , "Person bound to feudal lord" , "Lowly worker" , "Subject" , "Feudal tenant" .)