Why cheer him?
He plays for the opposing team. I don’t mean target him for booing, but he is just one of the opposition now.
He scored the most important goal in our history, certainly, but time has moved on. He gained our gratitude when he was with us, he lived off that for a while longer than his performances for us merited, and now is one of a team that is hoping for us to lose. If he isn’t wanting that then he has no place in their team.