Championship outfit Leeds have already knocked Everton and Tottenham Hotspur out of cup competitions this season.
With that in mind, the Argentine has insisted that City cannot afford to take their opposition lightly at the Etihad Stadium.
"I think it is going to be a really difficult game because Leeds have already proved they can beat anyone on their day," he told the club's official website. "They have beaten Spurs and Everton this season and it was only a couple of years ago they beat United at Old Trafford so we know they will give us a tough 90 minutes.
"They are bringing 6,000 fans and they will really lift the Leeds players and male plenty of noise. As we know, there are no easy games in the FA Cup, especially at this stage.
"Leeds are doing OK this season and they are a club who are set up for the Premier League so, like I said, we'll have to be at our best for this game."
The two sides have not met since March 2004, when Leeds ran out 2-1 winners at Elland Road.