A shortage of goals has been Manchester United's [Images] biggest problem in their fruitless pursuit of English Premier League leaders Chelsea, manager Alex Ferguson says.

United are unbeaten in their last 21 league games but, missing their usual ruthless streak in front of goal, trail the champions-elect by 13 points.

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"We've had a good season in respect of the points tally. Where we are disappointed is that our goals tally is not great. Forty-eight goals is not good enough for us," Ferguson told reporters on Friday.

"I can't understand it. We've missed a lot of chances and we missed Ruud [Van Nistelrooy] for a long period, but it's just unusual.

"If you look at our goals-for tally over the last decade it's fantastic. It's almost double what we've got at the moment.

"Hopefully, that kills itself at the end of the season and we can go on to do what we are normally good at, scoring goals."

United have failed to score in eight league games this season, including their opening match when they lost 1-0 to a Chelsea side who have never looked back.

"You've got to give credit to Chelsea's great season," the United manager added.

"They have won so many games 1-0, which is exceptional and unusual and may never happen again.

"They may win the next seven games 1-0 and I think that's very much part of their game-plan, not to lose goals."

United's shortage of goals has come despite spending over 30 million pounds last year on strikers Wayne Rooney [Images] and Alan Smith.

Though Smith has missed part of the season with injury they have scored only 14 league goals between them, while Van Nistelrooy is likely to fail to register 20 in a season for the first time in four years at Old Trafford.

The Dutch international has not hit the target in seven appearances since returning to the side in February following a three-month injury layoff to face AC Milan in the Champions League.

"It was worth taking a risk at the time. His record in European football in particular meant we expected him to deliver in the AC Milan game," said Ferguson, who retains complete faith in the 28-year-old.

"He's one of the best goalscorers in the business, probably one of the most clinical finishers we've had at this club.

"Obviously when you don't score, strikers do have that confidence thing that they only feel better when they are scoring goals and Ruud's not any different from anyone else."

Ferguson will have an extra attacking option for Saturday's trip to bottom club Norwich City, with French international Louis Saha back in the squad following a knee injury.

Ryan Giggs (hamstring) and Darren Fletcher (knee) miss the trip to Carrow Road as United look to return to second place ahead of Arsenal [Images] after being held to a 0-0 draw by Blackburn Rovers at Old Trafford last Saturday.

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