Silva will start for City at the Etihad.
"United have to try to stop [David] Silva somehow," Fletcher told the BBC. “And for them to do that, I think Ander Herrera has to play.
“Having been in the United dressing room with him, he is one of those players who remembers everything the manager says, and is constantly reiterating those points to the rest of the team.
“Not every player does that, because some of them are so tied up in the game themselves, but Herrera does not just remember his role, he remembers other people's too.
“He is that influential to the whole team, plus he is aggressive and he can set a tempo for United when they get the ball back.
“I like him and I would have him in the team. He could go up against Silva and make it a difficult game for him, which does not happen very often."