The Brazilian forward was sold to Flamengo during Allegri's first season at the San Siro and has claimed he had no option but to quit the club.
“I am a player that always wants to play, but many times Allegri left me out,” said Ronaldinho.
“This left me very upset. I was in good shape when I was at Milan but he didn’t play me to give me the opportunity to express myself, so that is why I left."
Rino Gattuso made similar claims earlier in the week saying that "locker room was out of control" under Allegri. The 2006 World Cup winner has recently moved to Sion.
"The locker room was out of control in the last two or three months with things I’d never seen in 13 years with the Rossoneri,” said Gattuso.
“The rules were no longer respected and the older players, who were irritated, no longer had the strength or the willpower to tell their teammates off. At that point I realised it was time to leave, even though the contract renewal was already prepared.
“When we had training at 9.30am, many arrived just 10 minutes beforehand and nobody would say anything. I’d arrive 45 minutes early in order to do some exercises, get a massage or even just to relax with a cup of coffee. That’s the sporting culture you get after years of experience.
“Or, when we had lunch at 13.00, some turned up 15 minutes late. There was no respect for the rules."