Sir Alex Ferguson was known for his 'hairdryer' treatment of players from time-to-time and Rio Ferdinand has revealed that seeing it on full blast at Ruud van Nistelrooy quickly made him realise the significance of the Manchester derby.
Ferdinand signed for Manchester United in July 2002 from Leeds United in a £30million deal - a then British-record. And just four months later he got his first taste of a Manchester derby as United travelled to local rivals Manchester City.
However, his derby debut didn't go to plan as Ferguson's side were swept aside 3-1 at Maine Road - with Shaun Goater scoring twice in the victory.
But despite the pain of the defeat, it wasn't until Ferdinand got into the supposed sanctuary of the changing rooms that he witnessed at first-hand what the derby should represent to United.
Reflecting on one incident, Ferdinand recalls Van Nistelrooy's appearance with a City shirt in his hand that sent Ferguson over the edge.
'We got beat 3-1 at Maine Road with Shaun Goater scoring two goals,' he told his Rio Ferdinand Presents FIVE YouTube channel during an interview with City legend Vincent Kompany.
'That was the first derby I played and the moment I realised how big it was was in the changing room after.
'We walked in and the manager shut the door. It was quiet and then all of a sudden he just erupted.
'Ruud van Nistelrooy, who was the God then, walked in with a City shirt in his hand and I remember Sir Alex Ferguson just absolutely unloaded on him. He destroyed him saying "if I ever see any of you walking with a City shirt ever again you'll never play for this club".
'That's how he was, he was just mad. That's when I sat there and thought "this is a big game, isn't it".
'I didn't realise before that game and ever since then, whether you win more or less, I knew that week leading up to a derby was all or nothing.'
Van Nistelrooy did atone for that faux pas in the return fixture in February by scoring at Old Trafford but Goater's 86th-minute header saw City earn a 1-1 draw - a fixture that Ferdinand was also a part of.