#3 Lack of attacking flair in the Team's style of play
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Yes, here it is, Mourinho's Manchester United is boring. While it may well have become a cliche by now, there is certainly some truth to this. Mourinho's teams have a tendency to search for the winning goal and, once scored, sit back and look to defend that lead.
With a strong defence, this tactic can certainly be successful. But a strong defence is something that United do not have. Arguably, the best defender is Eric Bailly and even he was benched repeatedly last season, apparently because he wasn't going to play in the World Cup. So, yes, that tactic does not work and even when it does, it is a marked deviation from the free-flowing, attacking playing style Manchester United has long been associated with.