Hargreaves faces five weeks out
Ferguson's selection for Saturday's 2-1 win over Wolves was affected by a virus that ruled out Dimitar Berbatov and left Nemanja Vidic, Patrice Evra and Paul Scholes weakened but able to play.
"We've no idea at all (on the team for Wednesday)," Ferguson said at a pre-match news conference on Tuesday. "We've still got some players out with 'flu and some players were sent home yesterday.
"So we're not in a great position at the moment. Hopefully tomorrow we're better, but there seems to be a lingering aspect of this virus going around and there's nothing we can do about it. We've a strong squad and we just carry on."
Midfielder Owen Hargreaves, who lasted just six minutes in his comeback from long-term injury at the weekend, faces up to five weeks out with a hamstring problem.
The 29-year-old England international, who has battled chronic tendinitis in his knees, made his first start in more than two years in Saturday's 2-1 victory at home to Wolverhampton Wanderers but soon left the field shaking his head at his misfortune.
Ferguson told local radio station Key 103 on Tuesday that the player was unlikely to play until mid-December.
"We're at that stage where we're sure his knee is OK," Ferguson said.
"His training performances in the previous eight or nine days were terrific. He had done really well, which is why we took the chance. But maybe the tension in the buildup for the lad was too much and he suffered because of it."
Hargreaves joined United for 17 million pounds from Bayern Munich in 2007 but has become the club's forgotten man.