Next to go in leads off (9)
I believe the answer is:
alongside
'next to' is the definition.
(I've seen this before)
'go in leads off' is the wordplay.
'off' indicates an anagram.
'go'+'in'+'leads'='goinleads'
'goinleads' anagrammed gives 'ALONGSIDE'.
(Other definitions for alongside that I've seen before include "Lying close to" , "Side by side" , "next door" , "Bordering" , "Aligned so as to be next to, as ship moored to pier" .)