Martin O'Neill believes Sir Alex Ferguson was wrong to leave Roy Keane out of his list of Manchester United's 'world-class' footballers.
In September, Ferguson insisted he had only managed four such players during his 27 years as manager at Old Trafford.
The Scot claimed Eric Cantona, Ryan Giggs, Cristiano Ronaldo and Paul Scholes were the only world-class players who played under him at United.
However, O'Neill, who has guided the Republic of Ireland to Euro 2016 with Keane as his assistant, said: "Roy's an iconic figure, and he's been a world-class footballer, regardless of what Sir Alex Ferguson says.
"He was a world-class player because he influenced that great Manchester United side like you wouldn't believe.
"He was the driving force of the team and when you are winning leagues and big cups and you have a driving force like that, I'm sorry but you can be classed as nothing else but world class."
O'Neill has six months to finalise his squad for the finals and has said he will keep a place open in his final 23 for Aiden McGeady even though the winger has hardly played for Everton in recent months.
He said: "McGeady was a massive part in the early part [of qualifying] and we owe him an awful lot. His goal in Georgia was fantastic, two goals, but the one that gave us three points was massive at the time and I don't forget those particular things.
"We have one or two players who have been in and around the squad and been excellent in their approach and loyalty. We have some games coming up in March and it might be a case they get an opportunity to stake a claim."