The Coalition's byelection campaign for Eden-Monaro is in chaos after prospective Liberal candidate Andrew Constance withdrew his nomination following a hostile personal attack by state Nationals leader John Barilaro, and doubts about whether he could have won preselection.

Mr Constance's withdrawal paves the way for local conservative Fiona Kotvojs to secure the Liberal nomination when preselection closes on Friday. Ms Kotvojs almost won the seat at last year's federal election, losing to Labor's Mike Kelly by 0.9 per cent.