Sir Alex Ferguson wants to rid Manchester United of the "achilles heel" of conceding first this season. Now the heavy winter period is here the manager is conscious he needs to solve the side's defensive issues.

After falling behind in six Premier League outings, United have managed to win five, the latest the 3-2 win at Aston Villa last Saturday from a two-goal deficit.

Ferguson, who takes his side to Norwich City on Saturday, said: "After last Saturday's experience we don't want to be losing two goals and having to fight back all the time. It is certainly an achilles heel this season. The fact we have players who can change the course of a game has certainly been a big advantage to us. Javier [Hernández] came on last week and changed the game completely. He should start."

The Mexican entered at half-time to score twice and may yet be awarded a hat-trick if his finish via Ron Vlaar is given to him. But Ferguson said: "We are conscious of the defending part. There is no consistent theme to it. We had to hold our hands up for the second at Villa; it was poor defending. It isn't a severe worry for me. It will improve."

Ferguson added that comeback victories can offer a lift. "The dressing room is different when you get these late goals or you come from behind," he said. "It does make an impact on the dressing room. There is more excitement. We have experienced that many times. Credit to the character of the club that we can do it.

"You don't expect to be behind by two goals. You always find that part difficult. It is not that we underestimate anyone, we just don't expect a Manchester United team to be two behind. You go into games believing you will be two ahead rather than two behind. It has happened a few times this season."

Ferguson said that Wayne Rooney's ankle injury and Jonny Evans groin problem mean there are "doubts" over the pair for Norwich, though Robin van Persie "should be fit" after a thigh issue. Regarding Phil Jones, who is recovering from a knee injury, Ferguson said: "He has been training all week. I am going to take him to Turkey [for the Champions League group game against Galatasaray]. He will get part of the game, which is a good start for him."

Rio Ferdinand, whose contract ends next summer, stated that he may wait until then to decide his future but Ferguson said: "It will sort itself out I am sure."

Regarding Paul Scholes, who turned 38 on Friday, and whether he will play on next season, the manager said: "It is not a time to make a judgment on that. Paul will know himself. He is still the best passer of the ball in the country. That has not stopped. He still has the desire to play. It is amazing. He made a fantastic contribution last year in the second half of the season. I just think he should keep doing what he is doing. He will sort it out himself."