Pack animal has problem with tendon (8)
I believe the answer is:
ganglion
'problem with tendon' is the definition.
I can't judge whether this definition defines the answer.
'pack animal' is the wordplay.
'pack' becomes 'gang' (synonyms).
'animal' becomes 'lion' (I've seen this before).
'gang'+'lion'='GANGLION'
'has' is the link.
Can you help me to learn more?
(Other definitions for ganglion that I've seen before include "Nerve centre" , "Swelling" , "centre of interest" , "Collection of nerve cells" , "A longing for group of nerve cells" .)