Manchester United boss Alex Ferguson has admitted his team's sudden loss of form is causing some head-scratching at Old Trafford.

Despite having a squad ravaged by injury, United romped through November and the early part of December winning eight matches on the trot and extending their unbeaten run to double figures. They went into the festive period well placed for a sustained championship challenge and with all their key men ready to return.

However, in just five days, the wheels have come off in spectacular fashion, Ferguson's side slipping to successive defeats at Blackburn and Middlesbrough to leave them an imposing seven points adrift of title favourites Arsenal ahead of today's visit by Birmingham.

Even more confusing for Ferguson is that the recent setback has coincided with the return to fitness of influential captain Roy Keane, key midfielder David Beckham and record-signing Rio Ferdinand.

"It's difficult to relate what is happening now with what has gone on before," he said. "When we went on our winning run we only had 12 players to pick from. Now the injured ones are coming back we start to lose. I don't know whether it's coincidence, but it is a strange situation."

Ferguson knows that United must collect six points from their next two home games if they are to retain any realistic hope of catching the Gunners. That, though, will mean the Old Trafford chief inflicting festive misery on two old friends in Steve Bruce and Howard Wilkinson.

The friendly rivalry with Wilkinson, which goes back to Ferguson's first days in English football after his arrival from Aberdeen, will be renewed after a six-year break when Sunderland visit on New Year's Day.

But when Bruce travels north with his Birmingham side today, the United manager will be facing an opposition boss steeped in Old Trafford tradition.

The rock-hard Geordie was a key figure in so many United triumphs under Ferguson's management down the years and is guaranteed an emotional welcome from the home faithful, even though he will take an unfamiliar place in the visitors' dug-out.

Ferguson has been impressed with the impact Bruce has had at St Andrews and, as the mid-point in the season slides by, is tipping the Blues to ensure Premiership survival.

"Birmingham are a determined and enthusiastic side, which reflects the traits of their manager," said Ferguson. "Steve has done very well there and they have a great chance of staying in the Premier League because they are consistently getting decent results.

"Any team who comes out of the first division always finds it difficult. There have been one or two exceptions like Ipswich, but even they went down the following season.

"It is important to get off to a good start which is exactly what Birmingham did. That will allow them gather experience as they go along. If you have a bad start, you don't have the experience to recover."

Ferguson is threatening to freshen his team up after the disappointment of the Christmas period, although he will have to take a late check on Mikael Silvestre to see if his French defender has recovered from the neck injury which kept him out at the Riverside.

Keane will also be monitored closely for signs of fatigue after his first full game in four months, while Beckham is ready to start after a recent stint on the bench.

"It has been frustrating to lose these last two games especially because we have been in complete control of both," said Ferguson. "They were two difficult matches and we won't be the only teams to find it difficult at Blackburn and Middlesbrough.

"But we have been caught on the counter-attack and conceded goals right before half-time, which is a killer. It is vital we get back on a decent run now and win our next two games. Home form is so important this season because the league is so tight.

"There is a huge determination among a lot of the teams to stay in the Premier Division and you are not seeing many big scores now. I will look to see if I can freshen things up by bringing in one or two players.

"Roy Keane did remarkably well yesterday, but it was his first game in a long time and we will need to check how he has come through it. Generally, there is a bit of tiredness in the squad, but you are going to get that at this stage of the season."

Bruce will have take a patched-up side back to his former stomping ground after picking up four more injuries - Steve Vickers, Damien Johnson, Geoff Horsfield and Jovan Kirovski - in the St Stephen's Day draw with Everton.

But the Birmingham boss is determined not to sit back as he knows this is likely to be fatal given the attacking qualities of United as he looks to extend his own side's impressive run of just one defeat in the last seven games.

"I had some great times there," he said. "It will be great to be going back. It's taken a long, long time to get there. I've never been back for a competitive fixture and I am looking forward to it immensely.

"When you are playing two games in three days, like everyone is at present, you hope for the second game to be at home with the crowd and the impact they can have.

"The most difficult time is when you are playing away and it's doubly difficult when that second game is at Old Trafford. But it's better than last year and playing in Division One.

"I would never bet against United and, if you sit back with the number of exceptionally talented players they've got, then it's impossible to defend against them for 90 minutes.

"What I've got to say to my players is let's go and enjoy it - and let's go and have a go at them. We've got to take that approach into the game.

"If we sit back and just accept things, then they are going to score. Let's take the fight to them - which is the way I always want my teams to try and play."