Liable to be left face down (5)
I believe the answer is:
prone
This clue might be a double definition.
'liable' is the first definition.
(both can mean having a tendency for something)
'face down' is the second definition.
(I've seen this before)
'to be left' acts as a link.
I am not very happy about this link. Some or all of it may belong to one of the definitions.
Can you help me to learn more?
(Other definitions for prone that I've seen before include "Showing a tendency" , "Lying face downward" , "Lying flat" , "Lying face downwards" , "Recumbent, likely" .)