The 21-year-old has made just two appearances for Les Canaris this term after suffering with a strained thigh.
Cetto was inching towards a first-team comeback after returning to training a fortnight ago but he has suffered a relapse in his rehabilitation.
The promising stopper tore the thigh muscle in training and has been ruled out for two months with the fresh setback.
Meanwhile, Nantes are expected to step up their interest in teenage striker William Diom after the Liberian impressed during a trial.
Diom represented Nantes' reserve side on Saturday in a bid to convince coach Lioc Amisse he is worthy of a contract.
The young African shone during the display and the French club are tipped to sign Diom during January's transfer window.
Nantes are also close to having Romanian starlet Claudiu Keseru at their disposal as they expect Fifa to ratify the forward's contract.
Keseru joined Nantes from Ordaea earlier in the season and agreed a three-year contract but Fifa expressed doubts about the deal due to the player's age before relenting on their stance.
