Spotted in nude, wrong is only alleged (9)
I believe the answer is:
unfounded
'only alleged' is the definition.
(as in an unfounded allegation)
'spotted in nude wrong' is the wordplay.
'spotted' becomes 'found' (spot can mean to find or locate visually).
'in' means one lot of letters goes inside another.
'wrong' is an anagram indicator.
'nude' with letters rearranged gives 'uned'.
'found' placed inside 'uned' is 'UNFOUNDED'.
'is' acts as a link.
(Other definitions for unfounded that I've seen before include "not established" , "Like Rome before 753 BC" , "no truth in it?" , "Baseless" .)