Blood-suckers left runny cheese (7)
I believe the answer is:
leeches
'blood-suckers' is the definition.
(I've seen this before)
'left runny cheese' is the wordplay.
'left' becomes 'l' (common abbreviation).
'runny' indicates anagramming the letters (I've seen this in other clues).
'cheese' with letters rearranged gives 'eeches'.
'l'+'eeches'='LEECHES'
(Other definitions for leeches that I've seen before include "drains resources" , "Bloodsuckers" , "Physicians once" , "Bloodsucking parasites" , "Blood-sucking worms once used by doctors" .)