De Assis said Ronaldinho and Kalil will give a joint press conference on Wednesday when the player's future plans will be revealed.
"He will play until he's 42! He will reveal his future destination on Wednesday," said De Assis, according to the Globo Esporte website.
Ronaldinho has been heavily linked with a move to Argentine giants Boca Juniors in recent days.
The 34-year-old has been identified as a potential replacement for Juan Roman Riquelme who left the club last week to join Argentinos Juniors.
A more fanciful rumour earlier in the summer linked the two FIFA World Player of the Year with Premier League outfit Stoke City.
Other reports have touted the MLS as a destination, while Brazilian club Fluminense are reportedly interested in taking him on.
The former Barcelona and AC Milan midfielder Ronaldinho joined Atletico in June 2012 and won the Libertadores Cup with them a year later, the first time he or they had lifted South America's biggest club trophy.
However, their title defence was a disappointment and they were knocked out in the last 16 by Colombian side Atlético Nacional.
They are also only 10th in the Brazilian League table, although the tight nature of the league means they are just five points off the leaders.
However, Ronaldinho has figured little this season due to a combination of poor form and injury.
"I can't call on Ronaldinho anymore," Atletico Mineiro coach Levir Culpi told SporTV. "His cycle with us has ended.
"It's unfortunate because he's an idol to all of us. Everyone loves his football, the way he plays and he's a very charismatic person.
"But that's the way it goes. He's leaving and we must move on without him."
Ronaldinho won 97 caps for Brazil, winning the World Cup in 2002, but was not part of the squad that competed on home soil this summer.