Vidic sustained a raptured cruciate ligament in United’s Champions League defeat to Basel on Wednesday.
The Serbian defender is now set to undergo surgery.
“We thought it was a bad one,” said United boss Sir Alex Ferguson. “He’s out for the season. It’s not unexpected, but it’s still bad news.
“He’ll see a specialist on Monday to work out the progress of when he has the operation. It won’t be immediate as we have to let the swelling come down.”
