Disadvantages seen when worker is about to go one better (9)
I believe the answer is:
handicaps
'disadvantages' is the definition.
(handicap is a kind of disadvantage)
'worker is about to go one better' is the wordplay.
'worker' becomes 'hand' (hand is a kind of worker).
'about' means one lot of letters goes inside another.
'to go one better' becomes 'cap' (I've seen this in another clue).
'is' going around 'cap' is 'icaps'.
'hand'+'icaps'='HANDICAPS'
'seen when' is the link.
(Other definitions for handicaps that I've seen before include "Disadvantages imposed on some competitors to equalise chances" , "Hampers" , "Advantages given to competitors to equalize chances of winning" , "Burdens imposed to level odds" .)