Sir Alex Ferguson has confirmed Nemanja Vidic's calf injury is worse than first thought with the Manchester United captain facing up to five weeks on the sidelines.
Central defender 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.
However, 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 regular defensive partner Rio Ferdinand seemingly 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.
"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.''
Ferguson will now pair Phil Jones and Jonny Evans together at the heart of his defence for the visit of Spurs, whilst Chris Smalling will fill in at right back.
Ferguson at least has Patrice Evra available again at left back after he missed the game at West Brom with a knee injury.