Man stood trembling, seeing such a creature (8)
I believe the answer is:
mastodon
'such a creature' is the definition.
(mastodon is a kind of animal)
'man stood trembling' is the wordplay.
'trembling' is an anagram indicator.
'man'+'stood'='manstood'
'manstood' anagrammed gives 'MASTODON'.
'seeing' is the link.
(Other definitions for mastodon that I've seen before include "dead hairy beast" , "Prehistoric creature" , "Huge animal" , "Old mammal" , "Extinct beast" .)