The current cup holders are looking to win the tournament for the fifth time in seven years.
The Chelsea midfielder told Sky Sports News: "It's a tournament that's been pretty good to us. We've just performed very well and we've got good success. That can change the minute you don't perform so well.
"Against a team of Man City's quality, you can't take any positives from previous history. If they're at their best, we're below our best, they'll probably win the game, and vice-versa. You're talking about two very good teams.
"We've got a lot of respect for them and I think it will be a good match, especially if both teams are at their best. You'll see a proper Wembley semi-final. I think they'll probably be on a high from their last result in the league, but other than that I think it's an even start with two good teams."
The winner of tomorrow's semi will face either Wigan Athletic or Millwall in the final.