Bound leaves up, with page slotted in (8)
I believe the answer is:
Here is my best explanation:
'bound' is the definition.
(strapping is a kind of binding)
'up with page slotted in' is the subsidiary indication.
'up' is a reversal indicator (in down clue: letters go upwards).
'with' means one lot of letters goes inside another.
'page' becomes 'p'.
'slotted in' becomes 'departs' (I can't justify this - if you can you should give a lot more credence to this answer).
'p' placed into 'departs' is 'depparts'.
'depparts' in reverse letter order is 'strapped'.
'leaves' is the link.
(Other definitions for strapped that I've seen before include "- - for cash (hard up)", "Secured; short of money", "Needy - secured", "Without, or very short of, money" and "Without, or very short of, cash".)