Nemanja Vidic has been ruled out for eight weeks following surgery on his knee.
The Manchester United centre-half was left out of Sunday's clash with Liverpool due to tightness in his left knee which was diagnosed as a meniscus problem and he has since had an operation which will keep him sidelined until after mid-November.
"Nemanja Vidic has had a meniscus operation on his right knee and will be out for around eight weeks," said a club spokesman.
"Sir Alex (Ferguson), as a precautionary measure, rested Vidic at the weekend, after he complained of tightness in his knee, however, further medical investigation revealed the underlying problem.
"The central defender was operated on this week and will be sidelined for about eight weeks."
