Lee's a pseudo supporter of the old master (5)
I believe the answer is:
easel
'supporter of the old master' is the definition.
'easel' can be an answer for 'supporter'. I am not certain of the 'of the old master' bit.
'lee's a pseudo' is the wordplay.
'pseudo' indicates an anagram.
'lees'+'a'='leesa'
'leesa' anagrammed gives 'EASEL'.
Can you help me to learn more?
(Other definitions for easel that I've seen before include "Framework to hold a canvas" , "Artist's canvas suppot" , "Support for 12's [ARTIST]" , "Support for artist's canvas" , "Stand in a studio" .)