Preview Arsenal v Man Utd
Mr. Ferguson has confirmed Ruud van Nistelrooy is "a serious doubt" for the FA Cup semi-final against Arsenal at Villa Park on Saturday.
Van Nistelrooy injured his knee in the Premiership game against Arsenal last weekend and it flared up while he was training with Holland this week.
"Ruud is a serious doubt," said Ferguson, who also has Louis Saha out as the Frenchman is cup-tied.
"It is looking very doubtful for him at the moment," added the United boss.
Both teams could therefore be without their star strikers as Arsenal boss Arsene Wenger is threatening to rest Thierry Henry ahead of next week's Champions League quarter-final second leg against Chelsea.
If Van Nistelrooy and Saha are both out, Diego Forlan will probably play even though he only returned from international duty with Uruguay on Friday.
Forlan could either play on his own up front or Ferguson could move Ole Gunnar Solskjaer, Paul Scholes, Ryan Giggs or David Bellion into a forward position.
"All we can do is hope there will be a change over the next 24 hours," said the manager about Van Nistelrooy.
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"It would be a bitter blow for us if he was to miss out because he is the man who can win us the game.
"We do have plenty of players who can replace him though Diego Forlan will go straight to the team hotel on Friday night."
Ferguson is prepared for a tough battle whichever team he puts out, following the edgy draw between the sides at Highbury last weekend.
"It's going to be a close game, there's no question about that," he told the club's official website.
"Nobody can say anything different, the evidence was all there on Sunday. "It will be a very close game, a difficult one to call."
United have a good Cup record at Villa Park - they have played four semi-finals there without defeat.
It has not all been rosy this season but we deserve to get to the final
Man Utd captain Roy Keane
Ferguson has led the Red Devils to victory in nine domestic semi-finals and if they win in Birmingham they will have reached their sixth FA Cup final since 1986.
"Our record at Villa Park is good and our support will be there which makes a difference," added Ferguson.
Captain Roy Keane is confident his side will put a stop to Arsenal's unbeaten run on Saturday.
The Irish midfielder believes the time has come for United to turn round their season, starting at Villa Park.
"It has not all been rosy this season and we have had one or two problems," Keane told MUTV.
"We deserve to get to the final but Arsenal probably think that too. Unfortunately someone's going to be disappointed."