Club president Pierre-Marie Geronimi confirmed in a video posted on Bastia's website that the Brazilian striker had been handed a jail sentence and a €20,000 fine, labelling the punishment "extremely harsh and severe".
It has been widely reported, however, that the sentence will be reduced so that Brandao must complete community service rather than serve time in prison.
Brandao headbutted Motta in the players' tunnel at Parc des Princes after PSG's 2-0 win over Bastia in August, breaking the midfielder's nose, with the forward having claimed on Monday that he was verbally abused by the Italy international throughout the match.
"The first reaction is that it is extremely harsh and severe," Geronimi said.
"A month in prison for an act he himself has expressed regret for and apologised publicly not long ago."
Geronimi apportioned blame to the French media as well, claiming they had played a significant role in the 34-year-old's conviction, while he also alluded to the allegations that Motta had "insulted Brandao for 90 minutes".
Parisian TV channel BFM TV reported that Brandao's lawyer Olivier Martin had also criticised the ruling.
"This is an extremely severe sentence compared to the criminal record of my client," Martin said.
"It's all the more severe because of the motivation that was raised by the President of the Court to justify the sentence.
"He referred to the violence in football stadiums."
Brandao did not appear in court on Thursday as the former Saint-Etienne striker was having surgery for a thigh injury.
