No longer performing on stage? That's tough (8)
I believe the answer is:
exacting
'tough' is the definition.
(I've seen this before)
'no longer performing on stage?' is the wordplay.
'no longer' becomes 'ex'.
'performing on stage?' becomes 'acting' (I've seen this before).
'ex'+'acting'='EXACTING'
'that's' acts as a link.
(Other definitions for exacting that I've seen before include "Requiring great effort - sounds precise" , "Insisting upon" , "Requiring great effort, arduous" , "Arduous and demanding" , "Tough" .)