Ronaldinho was very critical of Milan's performance against Juventus at the weekend, according to La Gazzetta dello Sport.
The Brazil international was left out of the key game at San Siro, raising questions about his future despite the niggling muscle injuries that have recently caused him problems.
La Gazzetta claims Ronaldinho was overheard at a bar in Milan's city centre questioning his team's recent tactics.
"We can't play like this way," he said.
"Ibra can't play on his own up front against four defenders."
Ronaldinho's brother Roberto De Assis, who also works as his agent, was later contacted by the paper and asked to reveal whether his client is angry.
"Sure, he's happier when he wins."
Ronaldinho's contract is due to expire in the summer and he has attracted interest from the LA Galaxy and Flamengo.