The Irishman made his name as a no-nonsense midfielder on the pitch while also commanding respect off it.
It's something Pique, who was only 18-years-old at the time, found out when his phone went off inside the changing room.
He explained to the Player's Tribune: "One of my very first matches at Old Trafford, we were in the dressing room getting ready, and I was nervous as hell.
"Imagine it - I'm 18 years old, and I'm sitting in that little dressing room putting on my socks next to Ruud van Nistelrooy, Ryan Giggs and Rio Ferdinand. I wanted to be invisible. I was thinking, 'Just do your job and go unnoticed'.
"So we're sitting there waiting for the gaffer (Sir Alex Ferguson) to come in and speak to us, and I'm literally sitting right next to Roy Keane.
"The dressing room is so small that our legs are almost touching. There's no space at all. It's dead quiet. All of a sudden, you could hear this little vibration. Very soft. Roy is looking around the room.
"I realise it's me. It's my cell phone. I left it on vibrate, and it's in the pocket of my pants, stuffed in the clothes bag that's hanging right behind Roy's head.
"Roy can't find where the noise is coming from. Now he's looking around the room like a maniac.
"He screams out to everybody, 'Whose phone is that?!'. Silence. He asks again. Silence. He asks a third time. 'Whose. Bloody. F***ing. Phone. Is. That?!' Finally, I spoke up, like a little boy. Very softly, I said, 'I'm so sorry. It's mine'.
"Roy lost his mind! He went nuts in front of everybody! It was incredible. I almost s**t myself. But it was a good lesson."
Keane would depart United in late 2005 after a falling out with manager Sir Alex Ferguson and signed for Scottish side Celtic.
Pique would remain at Old Trafford as an understudy to Rio Ferdinand and Nemanja Vidic before returning to boyhood side Barcelona in 2008.
The 34-year-old will go down as a legendary figure at the club having won eight La Liga titles and three Champions Leagues.
On the international stage, Pique helped Spain to World Cup glory in 2010 and Euros success two years later.
Keane paid tribute to Pique in his 2014 autobiography, writing per The Mirror: "Gerard Pique was a good lad and a good player. But he wasn't getting a run in the team and wanted to go back to Barcelona. He's done all right there!
"I don't think anyone could have predicted just how much he'd achieve. This theory that he isn't a good defender - he's one of the best."
Featured Image Credit: PA Images
Chosen for YouChosen for You
Most Read StoriesMost Read