The 41-year-old was found guilty of forgery, use of forgery and misuse of corporate assets by a Narbonne court on Friday, AFP, French sports daily L'Equipe and other media said on Friday.
A powerful blindside flanker, Elsom played 75 tests for Australia and captained the Wallabies from 2009 until just before the 2011 Rugby World Cup.
He also enjoyed a successful spell with Irish province Leinster and told Britain's Times newspaper in an interview on Sunday that he was teaching in a Dublin school.