Basel's second goal in the 3-3 draw on Tuesday night particularly concerned the boss, who knows Norwich will also look to exploit any gaps at the back at Old Trafford on Saturday. The Canaries are in good form and there is no danger of any complacency from the champions, particularly after what happened in the Champions League in midweek.
"Norwich have made a terrific start," said Sir Alex. "You look at Norwich and see full houses every week. There's something happening down there, a vibrance about the place.
"People say our performance on Tuesday was careless and we underestimated our opponents and maybe there's an element of truth in that. I certainly wasn't happy, even in the first half I could sense we were too relaxed. We could have lost three goals in the first 45 minutes. We could have scored goals as well but were too cavalier. People can enjoy the way we are playing and attacking at the moment but we have to do better defensively."
Despite the unbeaten start to the campaign, and a glut of goals, Sir Alex is aware that he may need to curb some attacking instincts in order to continue producing the right results.
"We have to balance both defence and attack and that's why it's called a team," declared the United manager. "A team functions in all parts, understanding each other's parts and we're too cavalier at the moment.
"We were far too cavalier on the second goal for instance. Patrice Evra was out wide tracking the boy who crossed it, Fabio was playing outside right, Phil Jones was in centre midfield. There was only Rio Ferdinand in the penalty box. I know it was a