Man in lab is working (5)
I believe the answer is:
basil
'man' is the definition.
(I've seen this before)
'lab is working' is the wordplay.
'working' is an anagram indicator.
'lab'+'is'='labis'
'labis' anagrammed gives 'BASIL'.
'in' is the link.
(Other definitions for basil that I've seen before include "Fellow" , "Doctor of the fourth century" , "Herb; forename" , "Plant; Brush; Fawlty" , "named Cardinal Hume" .)