I've written for years in these Forums that Michael blamed Tom for the decline of the Corleones and Sonny's murder. He removed Tom as Consigliere and relegated him to just certain parts of the family business and to being simply his lawyer ... until he really needed him. Then he lied to him. He also accused Tom of trying to leave the family and of not supporting him.

So, Tom could have realized that Michael thought he was disposable. Nevertheless, he might have tried to convince Michael to leave Fredo alone. I don't know. That's a tough call.