Former Republic of Ireland manager Brian Kerr believes that unless José Mourinho addresses his side's defensive shortcomings - they won't be able to challenge for the league title.
United beat Everton 2-1 t Old Trafford on Sunday and speaking to Off the Ball's Nathan Murphy after the game, Kerr said: "I think is tells you that they're not a great side - that there's a lot of edginess around the team which also surrounds the manager.
"There's a strange mood around. I think the supporters want the manager to be successful but they're frustrated with the results - they're frustrated with style of football. They've taken some hope out of the recent matches - Newcastle, the comeback second half - attack, attack, attack and they get three goals from 2-0 down.
"And last week against Chelsea - the manager, Mourinho - played as if they were hard done by when Chelsea equalised in the sixth minute of injury time. That wasn't the case.
"I felt Chelsea well deserved it - they were the better team for an hour in the match. United came back well and got two great goals. It was a poor performance during the week and they found out where they really are.
"Losing 1-0 to Juventus again - Manchester United and the manager played it as if they were unlucky not to get a draw but I felt they were well out-played in the match.
"Today, they were the better team, slightly. Everton, at times, showed some classy stuff. United showed some brilliant stuff - particularly from Juan Mata, Paul Pogba at times and Martial - who came up with a great second goal which ultimately wrapped it up for them.
"It never looked like the game was wrapped up but that second goal gave them the advantage that Everton couldn't quite match," he added.
Looking ahead, Kerr said: "Succesful teams are built on strong defensive units that are efficient. If you look at the best teams at the moment or the top two with Manchester City and Liverpool - Liverpool weren't solid enough defensively last year to really compete for the league. I think they finished 19 points behind Manchester City.
"Now, they look more solid - not conceding many goals. Manchester City obviously have been building a defensive structure for years and while the emphasis is on attack - they're still hard to score against. They've been buying expensive players, buying expensive full-backs. They brought in an expensive goalkeeper to make them more solid on the counter-attack.
"So, it takes time to develop that but it also takes the right players. With the back four that played today with David De Gea - will they become a unit that teams will struggle to score against? I somehow doubt it."
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