Millwall and Wigan contest the other semi-final and whoever progresses from that tie will be massive underdogs against City or Chelsea in the decider on 11 May.
"We are aware people are saying our semi-final is going to be 'the final', but that is disrespectful to Millwall and Wigan," said Zabaleta. "Nobody wins a trophy for winning a semi.
"The same thing happened when we played United in 2011 because Bolton and Stoke were in the other game.
"We need to beat Chelsea and then we can think about who we will play. It doesn't matter that Wigan and Millwall aren't considered top teams in that they are challenging regularly for major honours because in one game, anything can happen and it would all be about who plays the best.
"Our total focus right now is Chelsea who we know will be a very tough opponent, but we are in a good moment form-wise and if we play at our best we will have a great chance."
City defeated Chelsea at Wembley in this season's Community Shield and drew with them at Stamford Bridge before registering a 2-0 win at the Etihad Stadium in February.
However, Zabaleta says those games will count for nothing in Sunday's semi-final.
"Those results don't mean a thing - this is a different game and Wembley is a special place to play football and it gives everyone and extra motivation," he said.
"It's a very big pitch, too, so there are many factors to take into account on the day and they could have a bearing on what happens.
"I'm just looking forward to going back because the last time we played a semi-final (in 2011) there it was a fantastic occasion.
"For me, it was a special game because it was the first time I'd played at Wembley and to beat United as well was even better - I still have the battle scar on my thigh from (Paul) Scholes' high tackle to prove it!
"It was an incredible game and the celebrations from our supporters is something I will never forget.
"Obviously the final against Stoke was more important because we had a trophy to show at the end of it.
"We will prepare properly for Sunday and hopefully, things will go our way."