Mulumbu is also eager for his team-mates to put right October's 2-1 defeat by City in which the Baggies were heading for victory with ten minutes to go only to be undone by Edin Dzeko's late double.
"It's always exciting to play against a big side," he told the WBA website. "We don't even need the gaffer to speak a lot when you play against big sides.
"We will be ready to do something. We don't need to be scared about City or about United. We've shown some good things against big teams. I'm really confident and I hope we're going to win.
"I'm looking forward to playing against this team and that's a big test for West Brom to see where we are."