Inferior to a French wine knocked back (5)
I believe the answer is:
Here is my best explanation:
'inferior' is the definition.
'a french wine knocked back' is the subsidiary indication.
'a french' becomes 'un' ('a' transated into the French language**).
'wine' becomes 'red' (red wine is a kind of wine).
'knocked back' says the letters should be written in reverse.
'red' in reverse letter order is 'der'.
'to' is the link.
(Other definitions for under that I've seen before include "Less than", "Subject to the authority of", "See 7", "Beneath or subordinate to", "Governed by", "Anaesthetised", "Dylan Thomas wrote '. . . . . Milk Wood'", "Below, anaesthetised", "Subordinate to; planted with" and "Below or beneath".)