Chad accuses neighbouring Sudan of backing and arming insurgents fighting to topple Deby, a charge denied by Khartoum.
On Sunday the Chadian official said: "President Idriss Deby and Captain Mahamat Nour exchanged views on the possibilities of Nour returning to the fold [of the government side]."
If correct, the move by Nour, a former army captain whose FUC rebel forces carried out a daring raid on N'Djamena eight months ago, would be a propaganda boon for Deby's government, which has faced a spate of rebel attacks from the east this year.
There was no immediate reaction from the other rebel groups to Nour's meeting with Deby.
Security experts said Nour's return to the government fold might not lead to any lessening of rebel activity, because he had already broken with other anti-Deby rebel groups.
These other groups were continuing their rebellion against Deby's rule under a loose military alliance, presidency sources said.
At the end of November, Nour made a statement calling for a national political dialogue in Chad.
In contrast, the Union of Forces for Democracy and Development (UFDD), the Rally of Democratic Forces (RAFD), and the Platform for Change, National Unity and Democracy (SCUD) have intensified their military campaign against Deby in recent weeks, triggering heavy fighting in the east.