Slav is a poor actor (5)
I believe the answer is:
croat
'slav' is the definition.
(I've seen this in another clue)
'poor actor' is the wordplay.
'poor' indicates an anagram.
'actor' anagrammed gives 'CROAT'.
'is a' is the link.
(Other definitions for croat that I've seen before include "From Zagreb, perhaps" , "Actor (anag.)" , "One from Zagreb" , "eg Native of Zagreb" , "One of the races of former Yugoslavia" .)