Ferdinand pulled up in the warm-up at Stoke but United responded with a 1-0 victory, thanks to a late winner from Carlos Tevez.

The England international - who was replaced by Jonny Evans - will now miss the Barclays Premier League match against Middlesbrough on Monday at Old Trafford.

Ferguson said: "Rio suffered a back spasm, he has done it a few times this year.

"He will not be available for the Middlesbrough game. We have got to try and get to the bottom of the problem.

"But Jonny is an outstanding player. We are fortunate to have such a talented boy to call on.

"At 20 he shows such maturity. He reads the game well, he uses the ball well and his pace is good. He has all the attributes of a top player."

United took advantage after Stoke were reduced to 10 men when Andy Wilkinson was dismissed for two yellow cards in the 72nd minute.

Tevez scored from close range 11 minutes later after substitute Dimitar Berbatov crossed from the right of the six-yard box.

Ferguson said: "You start to worry a bit as the second half looked a bit of a stalemate. We had some chances in the first half.

"Then Dimitar showed great balance and turned the defender brilliantly before playing the ball across to Carlos to finish it off. We were delighted about that."

It was just the result United wanted as they are playing catch-up in the Barclays Premier League after being away in Japan, where they won the Club World Cup.

Ferguson was pleased with the way his side responded and shook off any lingering effects of jet-lag.

He said: "Hopefully we will look back and say this was a significant win for us.

"If we get to New Year's Day and are only a point or two away, then we will have a chance.

"I was pleased with the energy of the team. They were very bright just as they had been in training the past couple of days."

Ferguson admitted Stoke had given them food for thought.

He added: "It is not easy coming here. Stoke have beaten Arsenal and gone close against Chelsea and had some good results at home.

"They are doing their best to try and survive. It is very tight down there.

"Stoke are very resilient, determined and gutsy. However there is no question it was a sending off as it was a rash challenge by their player."

Wilkinson's dismissal cost Stoke dear and assistant manager Dave Kemp said: "It was not a smart thing to do, given he already had a card.

"It is hard enough to play against Manchester United with 11 men, never mind 10.

"I thought some of the bookings were unnecessary, though, as it was not a dirty game, just a good competitive game.

"To our credit we kept going and in my view we did well at both ends of the pitch."