Not suitable to put pan back into it (5)
I believe the answer is:
inapt
'not suitable' is the definition.
(I've seen this before)
'pan back into it' is the wordplay.
'back' says the letters should be written backwards.
'into' means one lot of letters goes inside another.
'pan' in reverse letter order is 'nap'.
'nap' inserted within 'it' is 'INAPT'.
'to put' acts as a link.
(Other definitions for inapt that I've seen before include "not seemly" , "badly judged" , "Inappropriate" , "Unsuitable - paint (anag)" , "Not suitable or appropriate" .)