United defender Mikael Silvestre will be absent in October as he nurses a metatarsal injury.
Assistant manager Carlos Queiroz confirmed the bad news on Friday, when he briefed the media ahead of this weekend's match against Newcastle.
"Mikael Silvestre's injury is more serious than we thought," said Carlos. "It's something in his metatarsal and he'll be out for six weeks."
Queiroz also said that Darren Fletcher and midweek match-winner Louis Saha have minor problems but both should be fit to face the Magpies on Sunday.
Better news comes through the recuperation of Ryan Giggs, who has started jogging as he bids to shake off a hamstring injury.
"HeÂ’s started individual runs, not with the team," revealed Carlos. "We think heÂ’ll be fine for Wigan. HeÂ’s doing well, his recovery process is nothing special and everythingÂ’s ok."
Queiroz feels that, regardless of which players feature on Sunday, both sets of fans can expect the traditional bout of goals and excitement against Glenn Roeder's Magpies.
"As far as I remember, Newcastle against Manchester always results in great, spectacular games with lots of goals," he said. "No matter which players are playing on Sunday for Newcastle or for us, it will be showtime for sure. ItÂ’s always like that."
Carlos is well aware of the need to return to winning ways domestically, after dropping points in the last two weekends against Arsenal and Reading.
"At the moment itÂ’s not important to think about Chelsea, Liverpool or Arsenal," he said. "ItÂ’s important to know we cannot drop points, especially in some games. Everybody knows that.
"Game after game weÂ’re going to fight as much as we can and fight as much as we can not to lose points as we did at Reading."
With Wayne Rooney continuing to attract media scrutiny after four games without a goal, Carlos revealed that the striker has been undertaking extra training to rediscover his form.
"ItÂ’s good that the player is conscious of his mistakes," he said. "Because what happens the day after is they come in with a better and a bigger desire to work more and more.
"This is what happened today. Wayne stayed for a while working alone, because he knows he needs to do something. But game after game, those things start to come right.
"Then the motivation and the confidence start to grow up, and he will establish his old game. This is what we believe will happen in the next game."