A viewer's problem may be left out of fashion (4)
I believe the answer is:
stye
'a viewer's problem' is the definition.
(problem with the eye, a 'viewer')
'left out of fashion' is the wordplay.
'left' becomes 'l' (common abbreviation).
'out of' is a deletion indicator.
'fashion' becomes 'style' ('style' can be a synonym of 'fashion').
'style' with 'l' removed is 'STYE'.
'may be' is the link.
(Other definitions for stye that I've seen before include "Viewer's complaint" , "Eyelid sore" , "Red eye" , "dump" , "swelling by organ" .)