Left, accepting bishop is yet to lose (8)
I believe the answer is:
unbeaten
'yet to lose' is the definition.
(I've seen this before)
'left accepting bishop' is the wordplay.
'left' becomes 'uneaten' (I've seen this before).
'accepting' indicates putting letters inside (inserted letters are accepted).
'bishop' becomes 'B' (chess abbreviation).
'uneaten' placed around 'b' is 'UNBEATEN'.
'is' is the link.
(Other definitions for unbeaten that I've seen before include "all-time" , "Not having lost a match" , "Undefeated" , "there's nothing better" , "Not defeated or vanquished" .)