Man in lab is suspect (5)
I believe the answer is:
basil
'man' is the definition.
(I've seen this before)
'lab is suspect' is the wordplay.
'suspect' indicates an anagram (a suspicious or unusual spelling).
'lab'+'is'='labis'
'labis' with letters rearranged gives 'BASIL'.
'in' acts as a link.
(Other definitions for basil that I've seen before include "Herb; forename" , "Herb; man's name" , "Boy - herb" , "Pesto ingredient" , "Saint" .)