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.
So, much is at stake in Sunday's huge showdown - but with no fans at Anfield, the clash between England's two biggest teams will lack the intense atmosphere of past encounters.
Not that it would have distracted Ferguson from his relentless focus on winning if he were still in the Old Trafford hotseat.
The 79-year-old claims he never let rival fans get under his skin when he took his charges on the road, as he would be concentrating too much on the game.
He admits there were too groups of supporters who made things "difficult" - but Liverpool fans weren't among them.
“You don’t really pay attention to that, your focus is on the game," Ferguson told A Team Talk with Legends when asked if there were any fans who 'worried' him.
"I remember arriving at one or two grounds when there was a bit of hassle, but nothing really serious.
"The grounds at West Ham and Leeds United were difficult, the fans were very vocal against us when we arrived, but during the game, the focus was too much on the actual game.”
United go into Sunday's clash having been led to the top of the table by manager Ole Gunnar Solskjaer, one of the heroes of United's two decades of dominance under Ferguson.
Solskjaer has guided his side to eight wins from their past 10 Premier League games - drawing the other two - while Liverpool need to recover their form having won just two of their last six.
