Present suppliers not entirely marvellous (4)
I believe the answer is:
magi
'present suppliers' is the definition.
(I've seen this before)
'not entirely marvellous' is the wordplay.
'not entirely' means to remove the last letter (not all of the word).
'marvellous' becomes 'magic' (I've seen this before).
'magic' with its final letter removed is 'MAGI'.
(Other definitions for magi that I've seen before include "Caspar, Melchior and Balthasar" , "Wise men, visitors to Bethlehem" , "Priests" , "The three Wise Men of the gospels" , "Sorcerers in ancient times" .)