Opening tender is an ugly sight (7)
I believe the answer is:
eyesore
'an ugly sight' is the definition.
(I've seen this before)
'opening tender' is the wordplay.
'opening' becomes 'eye' (eye is a kind of opening).
'tender' becomes 'sore' ('sore' can be a synonym of 'tender').
'eye'+'sore'='EYESORE'
'is' acts as a link.
(Other definitions for eyesore that I've seen before include "Something ugly and offensive" , "Ugly prospect" , "An unsightly thing" , "Ugly item" , "ugly feature" .)