A court official told Reuters that Elsom was found guilty of forgery, use of forgery and misuse of corporate assets by a Narbonne court last week. He has denied the charges.
Elsom, who was at Narbonne from 2013-16, was convicted in absentia and an international warrant has been issued for his arrest. He was also ordered to pay back 700,000 euros ($761,000).
Elsom said in a statement published by the Sydney Morning Herald on Tuesday that he had not been informed of the court hearing or given an opportunity to defend himself against the allegations.
He added that it was a "clear perversion of justice." The paper said Elsom had engaged a lawyer to appeal the court's decision.
A powerful blindside flanker, Elsom played 75 Tests for the Wallabies and captained them 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 this month that he was coaching at a Dublin school.
