Ferdinand, who returned from a three-month back injury lay-off against Hull, is due to meet Graham Bean, the FA's former compliance officer who now advises United on disciplinary matters, at their Carrington training ground on Wednesday morning to discuss the charge.
Related ArticlesMan Utd v Man City: match previewMan Utd swoop for SmallingFerdinand charged by FAReal: Wayne Rooney not a targetFerguson: my players will behaveSport on televisionFerdinand must respond by 6pm on Wednesday and it is understood that he will be urged to plead guilty.
United are, however, angry at what they perceive to be FA double standards. The club are bemused by the action against Ferdinand in the wake of the governing body's failure to charge Liverpool's Javier Mascherano for a similar incident involving Leeds forward Jermaine Beckford during a Carling Cup tie at Elland Road last September.
But with video evidence of Ferdinand's clash with Fagan, which was missed by referee Steve Bennett, the England defender is expected to reluctantly accept a three-game suspension, which would commence with the City game, rather than risk receiving a lengthier ban if any appeal is unsuccessful.
Sunderland defender Michael Turner and Middlesbrough forward Jérémie Aliadière have both been given extended suspensions by the FA in recent months on the basis of 'frivolous' appeals against charges of violent conduct.
By accepting the charge, Ferdinand will miss the game against City, Sunday's Premier League trip to Arsenal and visit of Portsmouth on Feb 6.
Should he deny the charge, however, he will be free to face City before learning his fate at a regulatory commission on Thursday.
United face City needing to overturn a 2-1 first-leg deficit, with Ferguson expecting Wayne Rooney to play a pivotal role for the home side. Rooney's four goals in the victory against Hull took him to 20 in all competitions this season.
Ferguson has claimed that United are aware of the external influences notably noises emanating from Barcelona and Real Madrid attempting to foment uncertainty over the Rooney's future amid growing speculation over his proposed new contract at Old Trafford.
Ferguson said: "I think we know where that [speculation] is coming from. In fact, we are sure where it's coming from. It's not his agent and it's not Wayne, so we'll deal with that.
"He wants to stay here. He has made that quite clear himself, but we already knew that he didn't want to leave here.
"He is in such great form and there aren't many players matching him at the moment. If he continues in this way he could get to 30 goals quite easily.
"He's got 20 now and the crucial part of the season is coming up, so he could easily get to more than 30."
While last Tuesday's first leg has been overshadowed by the verbal spat between City's Carlos Tévez and United's Gary Neville, both Ferguson and City manager Roberto Mancini have attempted to shift the focus back on to football ahead of tonight's game.
But with City chief executive Garry Cook claiming last week that the Eastlands club would ultimately be "bigger and better" than United, Ferguson suggests that his side's big-game experience is the perfect answer to those comments.
He said: "Sometimes people can get carried away. Only the future can decide that. But we have been in this situation so many times, coming into the second leg of a big semi-final needing a result.
"We've played some great teams over the years here Barcelona and Juventus in this sort of situation and we hope that experience helps us."
Mancini, who is set to name Emmanuel Adebayor, and possibly Kolo Touré, on the bench tonight, will become the first City manager since John Bond in 1981 to lead the club to a major final if his team avoid defeat at Old Trafford.
Despite the burden of expectancy, Mancini insisted his players are ready to break their cup hoodoo. He said: "After many years [without a trophy] we want to change the history.
"We want to get to the final and we have a good chance. We must keep our concentration. If you can stay calm, you'll play better."