Milan have long been linked with a move for Ronaldinho after the Brazilian was told he was not part of Barca's plans for the future.
"Yes, it's true, it's true that he'll probably go to Milan," De Assis - who is also Ronaldinho's brother - told Lombardy television stations. "Everything's ready for the transfer. He is there 80-90% and we are working towards that."
He added: "He is working hard to get back to his best and the important thing is that now he is fine and that he is working for his future."
Milan might be leading the pack but there is no shortage of other possible destinations for Ronaldinho, with Chelsea and Manchester City just two of the clubs reportedly in the hunt.
However, De Assis rubbished suggestions that the two-time FIFA World Player of the Year could join David Beckham at Los Angeles Galaxy.
"There's a contract with Barca, there's other possibilities," he added. "We'll see in the next fortnight.
"LA Galaxy? No, no, absolutely not. Why Galaxy?
"I absolutely rule out Galaxy. It's not possible because he is only 28 and he wants to play at least five or six years more at the top level in world football."