Said condition beginning to deteriorate (6)
I believe the answer is:
stated
'said' is the definition.
('state' can be a synonym of 'say')
'condition beginning to deteriorate' is the wordplay.
'condition' becomes 'state' (the state something is in).
'beginning to' indicates taking the first letters.
The first letter of 'deteriorate' is 'd'.
'state'+'d'='STATED'
(Other definitions for stated that I've seen before include "Expressed in written or spoken words" , "Declared or asserted" , "Set forth (in words)" , "Announced" , "Definitely expressed" .)