Ronaldinho had enjoyed a stormy relationship with former PSG boss Luis Fernandez but Graille is confident that he and new manager Vahid Halilhodzic can persuade him to stay, particularly as they are yet to receive a bid for the player.
"I don't doubt that one day soon, Ronaldinho will say to me 'I'll stay', said Graille.
"Discussions continue but I'm sure he will be in Paris next year. Moreover, I still haven't received an offer for him."
Sir Bobby is believed to be keen to sign the Brazil international, although Real Madrid and Manchester United are favourites for his signature.
Meanwhile Rennes striker Frederic Piquionne is the latest player to be linked with a move to St James’ Park, with Sir Bobby reported to have made a £2.25million bid for the player who scored 10 Le Championnat goals last season.