City chairman Thaksin Shinawatra is not in the country and has left the task of courting Ronaldinho and his brother to his close aides and board members Pairoj Piempongsant and Tawesuk Jack Srisumrid.
These two, along with agent Pini Zahavi, have been talking to De Assis in the last week and it is understood they continued their dialogue at a restaurant in the city after the match.
City boss Sven Goran Eriksson said: "I hope it's true. We're not protesting against that, but I've never heard that myself.
"I don't know if he wants to play in the UEFA Cup next season!"