Nur, a founder of the Sudan Liberation Movement (SLM), is currently living in France under an authorisation that expires at the end of the month, the diplomat said.
"His authorisation to stay will probably not be renewed due to his non-participation in the Sirte negotiations," said the diplomat, who declined to be identified.
New peace talks brokered by the United Nations and the African Union between Sudan's government and Darfur rebel groups in the Libyan city of Sirte stalled in late October. Most major insurgent groups boycotted the negotiations, saying they needed more time to fix their negotiating positions.
Sudan's state news agency Suna reported that French President Nicolas Sarkozy had given Nur a deadline to attend peace talks by the end of December or leave France.
An official at Sarkozy's office stopped short of such a comment, saying: "If Nur does not go to Sirte, the president will draw the consequences."