Ruud Van Nistelrooy has hilariously recalled Roy Keane taking issue with the Dutchman's customary headband.
Van Nistelrooy arrived at United in 2001 following a big-money from PSV, but he was not prepared for the ways of his new skipper.
"He led the team in an unbelievable way," Van Nistelrooy told Rio Ferdinand on the 'Vibe with FIVE' Podcast.
"He was direct, everybody knows that but in the beginning, I had to get used to that.
"For three months, every day he would talk about that hairband - 'get that thing out of your head! What the eff are you doing with that hairband? You're in the Premier League now!'
The 44-year-old added: "I remember the way he prepared for a game, I was shocked.
"He was just reading the programme, sitting there in the dressing room so calm and easy-going.
"He puts on his Diadorra boots with his big, round studs. He has the shin pads that are small with no ankle protection, no wrapping around the ankle.
"Then he jobs a few times around in the warm-up and the referee blows the whistle and then all of a sudden there is an animal on the pitch."
Van Nistelrooy, Keane and Ferdinand were mainstays in the United team during one of its most successful periods. But it was Corkman Keane whose attitude always stood out.
Rio added: "I used to say to all of my mates 'there's something wrong with him, there's something not quite right with him.
"Everyone else you could see getting ready [before games], getting into the mode. With him it was just like a switch.
"It was the same with the [Patrick] Vieira thing in the tunnel. In the changing room he was calm and quiet.
"And then in the tunnel he heard something and this animal came out, it triggered him."
