Sir Alex Ferguson has named the two sets of fans who worried him during his legendary stint as Manchester United manager. In Ferguson's 27 years as Red Devils boss, he achieved his stated aim of "knocking Liverpool off their perch" by winning an incredible 13 Premier League titles as his side became the dominant force in English football.
United travel to face their fiercest rivals on Sunday sitting top of the league in January for the first time since 2013 during Ferguson's final, triumphant campaign.
That season they would go on to win the last of their record top-flight 20 titles - with Liverpool just one behind after Jurgen Klopp's side rampaged to the crown last term.
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