An unknown obligation’s around that is causing concerns (9)
I believe the answer is:
Here is my best explanation:
'concerns' is the definition.
'an unknown obligation's around that is' is the subsidiary indication.
'unknown' becomes 'x' (algebra).
'obligation's' becomes 'ties' (I can't explain this - if you can you should give a lot more credence to this answer).
'around' means one lot of letters goes inside another.
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'xties' placed around 'ie' is 'xieties'.
'causing' is the link.