As filler, shortly check on old comedian (7)
I believe the answer is:
groucho
'comedian' is the definition.
(I know that Groucho is a comedian)
'as filler shortly check on old' is the wordplay.
I cannot quite see how this works, but
'check' could be 'ch' (abbreviation) and 'ch' is found within the answer.
'old' could be 'o' (common abbreviation eg in OE for Old English) and 'o' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for groucho that I've seen before include "One of four comedian brothers" , "One of Marx Brothers" , "The Marx Brother with the moustache" , "One of Harpo's brothers" , "Funny man" .)