Roy Keane frequently clashed with Vieira on and off the pitch during the pair's spells at Manchester and Arsenal respectively, but while bygones mightn't entirely be bygones, Keane insisted Vieira was as tough an opponent as he has faced.
"I don't think we'll ever be bosom buddies buying each other a drink in the pub but out of everybody I ever faced as a player, he drove me to become better.
"Obviously Arsenal were the team that really challenged Manchester United and, for a short time, went past us. And as their leader Patrick was immense.
"Without doubt I'd put him alongside Zidane, Scholes, Gerrard and Lampard as one of the very best I've ever played with or against, he was that good. On his day, when he was driving Arsenal on with the sheer force of his personality, he was unplayable."
Vieira's former Arsenal teammate Martin Keown was present at the event and admitted Vieira didn't always train like he played.
"You look at Denis Bergkamp and you look at Thierry Henry and people say they are great players and rightly so. There are statues of these guys outside the Emirates Stadium but without Patrick winning the ball and giving it to them they would almost be redundant.
"But sometimes during the week it was as if his non-football playing brother turned up for training instead, we used to call him Mr Floppy, but on a match day he was a different animal."