Hard-working, but missing us in workplace (6)
I believe the answer is:
studio
'in workplace' is the definition.
(I've seen this before)
'hard-working but missing us' is the wordplay.
'hard working' becomes 'studious' (studious can mean hard-working).
'but missing' is a deletion indicator.
'studious' with 'us' taken out is 'STUDIO'.
(Other definitions for studio that I've seen before include "Recording room" , "Here one may record" , "Workplace for production of film, say" , "Artist's place of work" , "Film company - artist's atelier" .)