Undermine Priam raving about Troilus at The Centre (6)
I believe the answer is:
impair
'undermine' is the definition.
(I've seen this in another clue)
'priam raving about troilus at the centre' is the wordplay.
'raving' indicates an anagram.
'about' is an insertion indicator.
'at the centre' means to look at the middle letters.
The central letter of 'troilus' is 'i'.
'priam' anagrammed gives 'impar'.
'impar' placed around 'i' is 'IMPAIR'.
(Other definitions for impair that I've seen before include "blunt" , "Weaken, damage" , "'Mar, spoil (6)'" , "Hobble" , "Spoil strength, quality of" .)