The defender last week returned to his first professional club after leaving Qatari side Lekhwiya.
However, his former employers have refused to release the 34-year-old's registration, leaving Nancy to await an international transfer certificate from FIFA before their new recruit can be cleared to play.
"That will take a bit more time," Nancy vice-president Nicolas Holveck told L'Equipe. "We hope it will be straightened out during January."
Explaining the situation that led to the dispute, Holveck added: "Given that the club he played for in Qatar (Lekhwiya) had not paid him for several months, the player unilaterally terminated his contract. The Qataris then refused to provide clearance for him to leave."
Ouaddou previously played for Nancy between 1999 and 2001 - before leaving for English side Fulham - but returned for two years from 2008. He spent last season on loan from Lekhwiya to Qatar SC.