He's a gold medallist (6)
I believe the answer is:
Here is my best explanation:
'medallist' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'he's a gold' is the wordplay.
'he' becomes 'vic' (short for Victor).
'a gold' becomes 'tor' (I can't explain this - if you can you should believe this answer much more).