Vialli was manager at Chelsea for two and a half years until he was dismissed in the early weeks of the 2000-01 season.
He said: "I think Rafael Benitez has finally realised it would be impossible to change the chairman's mind about giving him another season.
"I think he's also realised that there's no doubt the fans are not going to support him. I think he's done the right thing which is to ask the fans to forget about not liking the manager but to keep supporting the side and the players because the players need support. There's no doubt they're suffering a little bit from this situation."