Sir Alex Ferguson admitted his defence are suffering from inconsistency after Manchester United narrowly escaped a humbling at the hands of Basle.
The Swiss side were leading 3-2 - having come back from 2-0 down - only to see Ashley Young grab a last-minute equaliser on his Champions League debut to make it 3-3.
Basle also missed a host of other chances and Ferguson labelled his players "careless" and "lax".
He said: "There is still enough quality in the back positions - Evra and Ferdinand are very experienced. But you always like to have a back four playing consistently and we don't have that at the moment.
"It is not a problem for us because of the quality we have in the forward positions guarantees us goals, and we really should have put that to bed in the first half.
"I thought there was a carelessness about us throughout the game. The attacking part was very good at times - we played some very good football, particularly in the first half.
"But there was a carelessness about us and really, they could have scored three goals in the first half.
"I suppose in many ways, it is 'welcome to European football' because they were very lax for parts of the game. It's a wake-up call in many ways."
United had appeared to be cruising through two goals in 80 seconds from Danny Welbeck but the Swiss side, who had missed some clear chances in the first half, stunned Old Trafford to go 3-2 up.
Two goals from Alex Frei, one from the penalty spot, and one from his namesake Fabian Frei, saw United come close to their first home defeat for 17 months.
Ferguson insisted Italian referee Paolo Tagliavento had been wrong to award a penalty against Antonia Valencia for a foul on Marco Streller.
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He said: "We are disappointed with the penalty decision - I don't think it was ever a penalty kick, and a poor decision I felt.
"But it turned out to be a fantastic game with a great end in terms of excitement."
Basle coach Thorsten Fink - who was a player for Bayern Munich when they were beaten by United in the 1999 Champions League final - said: "It was a great result for us - I don't imagine many teams go two goals down here and then turn the game around. It was a great achievement.
"It was a great game for the fans, I think we were rather nervous in the first half but we settled down after the break and were able to take some chances.
"We deserved at least to draw and as a coach it feels good to come to a club like Manchester United and get such a result.
"The final in 1999 was more of a negative experience and I'm glad my team is able to celebrate tonight."
