In quarantine, the risk lower ... (6)
I believe the answer is:
nether
'lower' is the definition.
(as in nether regions)
'in quarantine the risk' is the wordplay.
'in' indicates a hidden word.
'NETHER' can be found hidden inside 'quarantine the risk'.
(Other definitions for nether that I've seen before include "Situated below" , "Lower in position" , "North European country" , "Lower, like regions or garments" , "These garments are for the bottom half" .)