Ferguson: Rooney out for two more weeks
Rooney has been absent since the 1-1 draw at Swansea due to the injury, which United initially expected to keep him out for a fortnight.
But he has still not been able to return to training and has now been ruled out of the trip to West Ham and the home game against Liverpool the following week.
Ferguson, who has struggled with defensive absences throughout the season, insisted his squad could cope with Rooney being sidelined but was frustrated to be without the England striker at such a vital period.
He said on Friday: "Wayne Rooney is still injured. We're surprised it's longer than we thought. We expected him back training but he's not. It's nothing serious but it looks as if he'll be out for another two weeks or so."
"He won't be fit for [the West Ham trip], I don't think. It's nothing serious, he just got clipped behind the knee, and we sent him for a scan but nothing really shows on the scan and he's still feeling it ... Hopefully two weeks will sort it but it's a loss and although we're in great form you want your best players available for the big games coming up ... We've got West Ham, Liverpool and Tottenham the week after that, and the FA Cup hopefully after that, so it's a tough period and you want your best squad available. We've not had that all season anyway so it's not as if we can't cope, we will."
The build-up to the weekend's action has been dominated by a training ground clash between Manchester City manager Roberto Mancini and striker Mario Balotelli.
The pair had to be pulled apart after a confrontation on Thursday and the incident was captured by watching photographers.
United's Carrington training ground borders City's but the Blues' property is surrounded by a public footpath that enables photographers to see in, despite large protective screens.
Even for Champions League away matches, United now train at Carrington whenever possible before flying abroad, rather than doing their work at the opposition stadium.
Training in private
Ferguson admitted that being able to train in privacy was vital for a manager.
He added: "You're protecting the possibility of your success. Do ICI send an email to Bayer chemicals telling them about their new discoveries in drugs or whatever? Do the major companies tell their opponents what they're doing? I'm sure they don't. Football has got a media profile and cameramen want to be at training sessions which I think is ridiculous ... It's very difficult for the coach to do work related to a game because you don't know where the information can go. It's a disappointment and it's hard for a coach."
"I think it's stopped at Real Madrid under José [Mourinho] but the press were in every day. It's what they expected and I know there are a lot of clubs in Italy where the press are there every day," Ferguson said.
"Fortunately at our place we can guard against that to a decent degree. Sometimes we get a photographer over in the woods but we've put these wolves in there! They never come now."
The United manager takes his side to West Ham for an FA Cup third round tie on Saturday.
Ferguson admitted he was frustrated by the club's recent record in the competition, which they have not won since 2004.
He said: "We've had some difficult ties and you hope you get a home draw and it's something you can navigate and get to the next round. The closer we get to Wembley the better we become.
"Rio has been with us 10 years and not won the cup – amazing. We'll have to do something about it." – AFP