Investigate possibility of ripping off patient (4)
I believe the answer is:
case
'patient' is the definition.
(synonyms)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for case that I've seen before include "Keep careful watch on" , "Legal action; box of wine" , "Overnight bag" , "Box of twelve bottles of wine" , "Humorous character" .)