Possible cause of upset in cabaret, I suspect (8)
I believe the answer is:
bacteria
'possible cause of upset' is the definition.
(eg cause of a stomach upset)
'cabaret i suspect' is the wordplay.
'suspect' indicates an anagram (a suspicious or unusual spelling).
'cabaret'+'i'='cabareti'
'cabareti' is an anagram of 'BACTERIA'.
'in' acts as a link.
(Other definitions for bacteria that I've seen before include "These single-cell organisms are in bait race" , "Possible cause of disease" , "Cabaret I found containing microscopic organisms" , "could make you feel bad" , "Microorganisms that can cause disease" .)