No amateur discovered to be intense (8)
I believe the answer is:
profound
'intense' is the definition.
('profound' can be similar in meaning to 'intense')
'no amateur discovered' is the wordplay.
'no amateur' becomes 'pro'.
'discovered' becomes 'found' (finding is a kind of discovering).
'pro'+'found'='PROFOUND'
'to be' is the link.
(Other definitions for profound that I've seen before include "Intellectually deep" , "anything but superficial" , "unqualified" , "showing great knowledge" , "deeply intellectual" .)