One severely criticised about nothing, abandoned by supporters (8)
I believe the answer is:
isolated
'abandoned by supporters' is the definition.
(one with no supporters or allies)
'one severely criticised about nothing' is the wordplay.
'one' becomes 'i' (Roman numeral).
'severely criticised' becomes 'slated' (slate can mean to criticise severely).
'about' indicates putting letters inside.
'nothing' becomes 'O' (O resembles 0).
'slated' going around 'o' is 'solated'.
'i'+'solated'='ISOLATED'
(Other definitions for isolated that I've seen before include "individual" , "Separated from others" , "Set apart, quarantined" , "Solitary" , "'Detached, kept apart (8)'" .)