The 30-year-old has been linked with a move to Flamengo in recent weeks.
“To the question that should Dinho like to one day to play with Flamengo, the answer is yes,” de Assis told Gazzetta dello Sport.
“This is his dream. But there is nothing else. We have not had contact and we have no intention to do this.
“Milan offered us a contract extension until 2013 and we agreed to talk about this by December. But the commitment for next season has never been under doubt.
“Our relationship with Milan is positive and my brother continues to think as he was two months ago: he wants to stay at Milan.”
De Assis hinted that Ronaldinho could decide to make a move to the USA when he leaves AC Milan.
“During the USA tour, we met a few people,” he added. “And (David) Beckham is pushing to get Dinho at LA Galaxy.
“Should an agreement not be reached for the renewal, this could be an option for next summer.”