Study that's barely sufficient, curtailed (4)
I believe the answer is:
scan
'study' is the definition.
(I've seen this before)
'barely sufficient curtailed' is the wordplay.
'barely sufficient' becomes 'scant' (I've seen this before).
'curtailed' means to remove the last letter.
'scant' with its last letter taken away is 'SCAN'.
'that's' is the link.
(Other definitions for scan that I've seen before include "MRI or CAT say" , "Look over (in order to copy?)" , "Look at quickly" , "Examine (to transmit)" , "at one's feet?" .)