Substitute essentially uninterested took a seat close to Benitez (6)
I believe the answer is:
ersatz
'substitute' is the definition.
('ersatz' can be a synonym of 'substitute')
'essentially uninterested took a seat close to benitez' is the wordplay.
'essentially' says to take the centre.
'took a seat' becomes 'sat' (I've seen this before).
'close to' says to take the final letters (the close/ending of).
The central letters of 'uninterested' are 'er'.
The final letter of 'benitez' is 'z'.
'er'+'sat'+'z'='ERSATZ'
(Other definitions for ersatz that I've seen before include "Made in imitation, from German" , "Inferior substitute" , "Phoney as in Germany" , "Imitation (from Ger.)" , "False" .)