Caution a director concealing low point (5)
I believe the answer is:
nadir
'low point' is the definition.
(I've seen this before)
'caution a director concealing' is the wordplay.
'concealing' says the answer is hidden in the clue.
'NADIR' can be found hidden inside 'caution a director'.
(Other definitions for nadir that I've seen before include "Drain into the lowest point (5)" , "worst-case scenario?" , "pits" , "least successful point" , "Low-water mark" .)