Ferguson, who has already seen Vidic’s central defensive partner Rio Ferdinand limp out of action this season, said the Serbian’s calf problem was worse than initially feared.
“The situation has reversed and Vidic has a calf muscle injury, which means he’ll maybe be four to five weeks,” Ferguson told reporters.
There was better news for Ferguson however with confirmation that Ferdinand may return sooner than anticipated after initially being ruled out for six weeks with a hamstring strain.
Ferguson said although the England defender would miss Monday’s clash with Spurs at Old Trafford, he may return to full fitness in time for United’s clash with Arsenal on August 28.
“Rio is not as bad as we thought and he could be ready for our game with Arsenal,” said the Scot.
“I don’t think he’ll be ready for Monday, but it’s amazing how assessments can change in the space of a few days.”
With Vidic and Ferdinand absent, Ferguson will pair new signing Phil Jones, 21, and Jonny Evans, 23, at centre-back against Tottenham, who have not won at Old Trafford since December 1989.
Although new United goalkeeper David De Gea has looked unconvincing in his opening two games for United, Ferguson said he had full confidence that his makeshift defence would be able to cope with a Spurs attack which smashed five goals past Hearts in their Europa League tie on Thursday.
“No worries, absolutely not,” said Ferguson.
“Evans has got ample experience, he’s been at the club since he was 12 and he’s played plenty of first-team games.
“Jones has got experience of playing for Blackburn last season and he and (Chris) Smalling, I thought were the stars of the England Under-21s this year [at the European Championship finals].
“De Gea will learn from the experience of the games he has had so far. There’s [Tom] Cleverley and [Danny] Welbeck too and it’s a very young team at the moment, but a team full of energy and a team with great ability. I’m enjoying watching them at the moment.”
With the retirement of Edwin van der Sar and Paul Scholes in the summer, Ferguson added: “We are always aware players were coming to an end anyway.
“You don’t want it to happen but it happens and nothing you can do about it. Age catches up with us all.
“We were confident with Welbeck and Cleverley coming back and we were determined to get Jones, from a way back, since last November, and also de Gea.
“We have replaced the players who have left us. At some point when the young players may hit a bit of a pocket, they will have enough experience with Ji-Sung Park, [Michael] Carrick and [Darren] Fletcher to augment the challenge what we are after this year.
“We are conscious of the future here in terms of making sure we have a nucleus of players who can play for a long time.”
Ferguson also has Javier Hernandez in contention after suffering concussion on United’s American tour.
“Chicharito has trained very well but when we decide to bring him back, it depends on a medical point of view considering he had a concussion before, when it’s safe to bring him back.”