McLean a problem in fetter? (7)
I believe the answer is:
manacle
'fetter?' is the definition.
(manacling is a kind of fettering)
'mclean a problem' is the wordplay.
'problem' indicates an anagram.
'mclean'+'a'='mcleana'
'mcleana' is an anagram of 'MANACLE'.
'in' is the link.
(Other definitions for manacle that I've seen before include "Curb" , "Metal shackle" , "Fetter" , "Shackle on the wrist" , "restricting at the cuff?" .)