Better to cover worker retiring for a short sleep (6)
I believe the answer is:
Here is my best explanation:
'a short sleep' is the definition.
('catnap' can be a synonym of 'short sleep')
'better to cover worker retiring' is the subsidiary indication.
'better' becomes 'cap' (I've seen this in other clues).
'to cover' means one lot of letters goes inside another.
'worker' becomes 'ant'.
'retiring' says the letters should be written in reverse.
'ant' reversed gives 'tna'.
'cap' going around 'tna' is 'catnap'.
'for' is the link.
(Other definitions for catnap that I've seen before include "(Tom's) snooze?", "Forty winks (for moggy?)", "Brief doze", "Snooze" and "Short sleep".)