Work-shy person —but not very — is one on a downward slope (5)
I believe the answer is:
skier
'one on a downward slope' is the definition.
(as in skiing down a slope)
'work-shy person but not very' is the wordplay.
'work-shy person' becomes 'skiver' (someone skiving off from work).
'but not' suggests deleting specific letters.
'very' becomes 'v' (abbreviation).
'skiver' with 'v' taken away is 'SKIER'.
'is' acts as a link.
(Other definitions for skier that I've seen before include "Slalom contestant, perhaps" , "He glides over snow, perhaps in sport" , "He glides across snow for fun" , "One up mountain, perhaps" , "he's possibly going downhill quickly" .)