Concluded great deal, though it might put them under too much pressure (8)
I believe the answer is:
overload
'pressure' is the definition.
(thesaurus)
'concluded great deal' is the wordplay.
'concluded' becomes 'over' (synonyms).
'great deal' becomes 'load' (I can't explain this - if you can you should give a lot more credence to this answer).
'over'+'load'='OVERLOAD'
'though it might put them under too much' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for overload that I've seen before include "tax" , "Put too great a demand on (electric circuit)" , "Weigh down" , "Burden excessively" , "Excessive demand (on a system)" .)