"He's out for the season. He sees a specialist on Monday, also to map out the progress of when he has the operation. It won't be immediate because we have got to let the swelling come down first of all," Ferguson told a news conference.
The Serbia centre-back was carried off on a stretcher during the 2-1 loss in Switzerland on Wednesday which sent United out of the Champions League at the group stage.
"When you saw the replays you realised it was a bad one," Ferguson added ahead of the Premier League match at home to Wolverhampton Wanderers on Saturday.
The 30-year-old Vidic left the St. Jakob-Park stadium on crutches and his agent said on Thursday the defender had "suffered a ruptured cruciate ligament".
"We'll now have to choose between Jonny Evans, Phil Jones and Chris Smalling [to replace Vidic]," added Ferguson.
DOMINANT CHARACTER
"I thought Rio [Ferdinand] had his best game of season on Wednesday. His experience will be vital.
"[It] is a loss and we missed him [Vidic] in the early part of the season for five weeks with his calf injury against West Brom.
"He's such a dominant character, particularly his defending in the penalty box. That's always a strong feature of his game."
There was better news up front where Bulgarian Dimitar Berbatov could be fit for the visit of Wolves with champions United looking to close the gap on leaders Manchester City to two points before their rivals visit Chelsea on Monday.
"All the rest who are injured are still out. We hope the turn of the year brings all these players back. They should be back by New Year."
Midfielder Tom Cleverley, strikers Michael Owen and Javier Hernandez and the Da Silva twins, defenders Fabio and Rafael, are all sidelined.
