The blue half of Manchester are currently two points clear of the Red Devils at the top of the Premier League table.
The 23-year-old England international, who has competed in ten Manchester derbies, believes that the Blues are capable of toppling Sir Alex Ferguson's side.
"United now know, much as they won't say it, that we are a genuine threat to them," Richards told the Manchester Evening News.
"We are not going out and saying we will win this game or that game, but they call us the noisy neighbours. I think they're a bit frightened."
The two sides go head to head at Old Trafford this Sunday.