Reds legend Paddy Crerand says United must concentrate for 90 minutes against Norwich or face a repeat of the shock midweek draw with Basel.
Crerand blames complacency for the Swiss outfit's startling comeback at Old Trafford on Tuesday, when they came within a whisker of a famous Champions League win before Ashley Young’s late leveller.
And MUTV pundit Crerand has warned that if the Reds are not completely on the ball on Saturday, Paul Lambert's improving Canaries could spring another surprise.
"The Premier League is a top-class football league and if you do anything daft you’re going to get punished," Crerand told ManUtd.com. "It’s the same in Europe – you need 100% concentration all the time.
"I never thought for one minute that Basel would get a result at Old Trafford, never mind score three goals. So you have to be alive all the time.
"Norwich are a young team who’ve come up to the Premier League and we saw the surprises Blackpool produced last season. They beat Sunderland last time out so they’ll be confident.
"You can’t win every game at home, no matter how well you’re playing, but I think United should get the points because we’re under a little bit of pressure from Manchester City.
"Sir Alex will make changes – he used a few experienced players against Basel and it’ll be interesting to see who’s fit for this weekend."