A case is to be made for a colleague (9)
I believe the answer is:
associate
'a colleague' is the definition.
(thesaurus)
'a case is to be made' is the wordplay.
'be made' indicates an anagram.
'case'+'is'+'to'='caseisto'
'caseisto' is an anagram of 'ssociate'.
'a'+'ssociate'='ASSOCIATE'
'for' is the link.
(Other definitions for associate that I've seen before include "Consort" , "Connect; partner" , "Partner, companion" , "Get together with" , "friend?" .)