Team captain Vidic limped out of the 2-1 win at West Brom last
Sunday, although it was initially anticipated a nerve issue would
keep him out for just two weeks.
Ferguson said: "The situation has reversed and Vidic has a calf
muscle injury, which means he'll maybe be four to five weeks."
There was some good news for Ferguson, though, with Vidic's
partner Rio Ferdinand looking set to return quicker than
anticipated from a hamstring injury also sustained at The
Hawthorns.
Ferguson's assessment at the time was Ferdinand would be
sidelined for six weeks, missing England's Euro 2012 double-header
against Bulgaria and Wales next month, as well as the start of
United's latest Champions League quest.
However, following a visit to a specialist in Munich during the
week, the injury is not as bad as first feared.
Although the centre back has not been definitively ruled out of
Monday's clash with Spurs at Old Trafford, it is more likely he
will be ready to face Arsenal at home six days later.
Fergie said: "Rio is not as bad as we thought and he could be
ready for our game with Arsenal,.
"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."