Old doctor's general companion? (5)
I believe the answer is:
leech
'old doctor's' is the definition.
(I've seen this before)
'general companion?' is the wordplay.
'general' becomes 'lee' (Robert E. Lee - US revolutionary commander).
'companion?' becomes 'ch' (I've seen this in other clues).
'lee'+'ch'='LEECH'
(Other definitions for leech that I've seen before include "Bloodsucking annelid" , "Proverbial bloodsucker" , "Bloodsucker; early doctor" , "Blood sucker" , "one good at sponging" .)