The announcement came after a troubled 17 months at Brazil's most popular club where the 32-year-old World Cup winner with the famous goofy grin has suffered a sharp drop in form since the start of the year.
"Ronaldinho is no longer a Flamengo player, his contract has been broken off in court," his lawyer Gislaine Nunes told Brazilian television.
Ronaldinho was jeered off the pitch when he was substituted on Saturday after a mistake led to Internacional's equaliser in a 3-3 draw in the Brazilian championship.
He was given permission to visit his mother, who has health problems, after the game but missed training this week and failed to join the team on a flight to Teresina in north-eastern Brazil for a friendly on Thursday night.
Flamengo said in a statement that Ronaldinho had missed training for four days in a row and that the matter would be handled by the club's legal department.
"We have always dealt with matters concerning Ronaldinho internally and with high standards," said club president Patricia Amorim.
"We didn't expect an attitude such as this. The legal department will take measures to protect the interests of Flamengo.
"The club is bigger than any person and always will be."
Earlier, football vice-president Paulo Cesar Coutinho told a group of supporters in the team hotel in Teresina that Ronaldinho had been dropped from the squad, although this was not confirmed officially.
Coutinho, whose comments were filmed by one of the fans, said Ronaldinho had been "playing rubbish".
Ronaldinho was voted FIFA's World Player of the Year in 2005 and 2006 but his career has been steadily going downhill since then and his drop in form is often blamed on his partying lifestyle.
He reached his peak during a five-year spell with Barcelona, then spent three less successful years with AC Milan before joining Flamengo at the start of last year.
He also peaked early at international level, helping to win the 2002 World Cup, performing poorly four years later and being left out of the squad altogether for 2010.
At the start of this year, coach Vanderlei Luxemburgo left Flamengo after a series of public disagreements with the player, who has also been criticised by Luxemburgo's successor Joel Santana.
Ronaldinho's brother and agent Assis has complained that Flamengo have not been playing Ronaldinho on time.