Business graduate in drag with old complaint (7)
I believe the answer is:
lumbago
'complaint' is the definition.
(I've seen this before)
'business graduate in drag with old' is the wordplay.
'business graduate' becomes 'MBA' (Master of Business Administration degree).
'in' is an insertion indicator.
'drag' becomes 'lug' (I've seen this in other clues).
'with' says to put letters next to each other.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'mba' put within 'lug' is 'lumbag'.
'lumbag'+'o'='LUMBAGO'
(Other definitions for lumbago that I've seen before include "Form of backache" , "Rheumatic pain in muscles of lower back" , "Rheumatic pain in the small of the back" , "Rheumatic backache" , "Back problem" .)