On-loan Peterborough striker Saido Berahino has returned to parent club West Brom after scans revealed the teenager has a chipped bone in his knee.
The injury is expected to keep the 19-year-old out for at least two months and, with Tyrone Barnett and Emile Sinclair on the transfer list and currently out on loan at Ipswich and Barnsley respectively, Posh boss Darren Ferguson will look to sign a replacement striker in January.
He told the club's official website: "It is a massive blow because Saido has made a real impact, but he is going to be out for at least eight weeks so has returned to West Brom.
"We will look at maybe bringing him back again when he is fit, but will have to remain patient on that one.
"We will be looking to strengthen in that particular area of the field in the new year."
Berahino joined Peterborough in October and scored two goals in 10 npower Championship appearances.
United and City are limping into the first Mancunian showdown of the season following midweek Champions League defeats.
Yet their dominance of the Premier League scene is such that the pair have already established a massive advantage over third-placed Chelsea.
United are 10 points clear of third, and City seven; enough for many pundits to declare this season's title battle a two-horse race.
Given the pair's scrap for honours last term was only decided in the last minute of the last game, when Sergio Aguero scored the goal that sent the Blues into ecstasy, it's little wonder the hype has started to go into overdrive.
But 39-year-old Giggs, who boasts a record 35 appearances in the fixture, refuses to lift City above any of the other fierce rivalries United have had down the years.
"It doesn't mean anything extra because it is City," said Giggs.
"There are different rivalries.
"Liverpool has always been the biggest rival for me. It has always been the biggest test.
"Arsenal were a brilliant team and we had some ferocious battles with them. Chelsea were also a brilliant team under (Jose) Mourinho and now City are a good team as well.
"The added dynamic is that they are on our doorstep. But we still want to win the league no matter who we are competing against."
It is well over two decades ago now that Giggs turned up for training at City's youth set-up wearing a United kit, eventually jumping at the chance to switch to the club he supported and has now made 920 appearances after captaining the Red Devils in their 1-0 Champions League defeat to CFR Cluj.
Until 2008, the thought City might actually deprive him of silverware was laughable.
Sheikh Mansour's deep pockets have changed all that, though.
And whilst Giggs agrees with Sir Alex Ferguson's assessment that Chelsea cannot be written off, the Welshman is aware how significant Sunday's game can be.
"We have found over the last couple of years that the derby, with the money City have spent and the quality they have brought in, has got bigger and bigger," said Giggs.
"The two games against them were the difference last season. Hopefully we can get the right result and that will be the difference come the end of this season."
It promises to be a fascinating occasion, not least because of the obvious flaws in their respective make-ups.
City remain unbeaten. Yet they crashed out of Europe altogether this week after the worst Champions League performance by an English club in the competition's history and have drawn three of their last six games in the Premier League.
United boast the league leadership, but in doing so have conceded 21 goals - more than relegation-threatened Sunderland - and Sir Alex Ferguson said earlier this week if there was any repeat of the appalling defending on show at Reading last weekend 'God knows what will happen'.
"We are both in a similar situation," said Giggs.
"We are in a good position in the league but haven't hit the form we did in parts last season.
"That can be frustrating because we want perfection.
"We want to be the best team and each individual wants to be the best player.
"We must be doing something right because we are in a good position and there is the belief we can score goals.
"But that doesn't mean we should neglect our defending and not try and stop the goals we are leaking because we need to stop conceding them."
It is a point Ferguson has drilled home countless times this season already.
And it is one that is steering the United boss towards a feeling Sunday's game will be a sterile affair.
"On paper, it is a match between the two best teams in the country," Ferguson told United Review.
"As the table tells us, there is not much between us.
"We need to come out unscathed and with so much at stake I wonder if there will be a little bit of caution from both clubs.
"Roberto Mancini and I will both have to think deeply about our selections and tactics and there may well be an element of playing safe."
