Manchester United captain Nemanja Vidic has been ruled out until Christmas, a month longer than Sir Alex Ferguson initially expected.
The Serbian had a meniscus operation on his right knee after the first Champions League group match against Galatasaray after Ferguson initially said he had rested him in the win at Liverpool due to him "feeling a bit tight round about his knee".
But further medical investigation "revealed the underlying problem", which lead to an operation and Ferguson has now added another month on to his expected comeback date.
"I think we're talking around December for Vidic," the Scot told MUTV. "Maybe around Christmas time."
Vidic made his first appearance in eight months in August after he sustained knee ligament damage in the Champions League defeat to Basel last year.
Chris Smalling, who was ruled out for 10 weeks in July after suffering a broken foot and Phil Jones, another centre-back who had knee surgery in September, are thought to be close to full fitness.
Rio Ferdinand and Jonny Evans have been ever-present for United at centre-half this campaign.
Scott Wootton and Michael Keane, two academy scholars, are Ferguson's back-up choices to Ferdinand and Evans, who started 23 games together last season.