Entering slump, unfortunate nick brings dismissal (7)
I believe the answer is:
sacking
'dismissal' is the definition.
(I know that dismissal can be written as sacking)
'entering slump unfortunate nick' is the wordplay.
'entering' indicates putting letters inside.
'slump' becomes 'sag' (I've seen this in other clues).
'unfortunate' indicates anagramming the letters.
'nick' with letters rearranged gives 'ckin'.
'sag' going around 'ckin' is 'SACKING'.
'brings' acts as a link.
(Other definitions for sacking that I've seen before include "Terminating someone's employment" , "devastating" , "made of hessian?" , "Looting - coarse cloth - dismissal" , "P45" .)