Former Manchester United, Leeds United and Ireland midfielder John Giles has no problem with Barcelona's Lionel Messi joining the pantheon of great players - but says Real Madrid's Cristiano Ronaldo is not yet welcome.
Although he calls the Portuguese winger a 'phenomenon', Giles says Ronaldo's temperament is what stops him joining the likes of Pele, Bobby Charlton, Diego Maradona and Messi.
"(It's) because of his attitude," the 72-year-old said in a telephone interview from his home in Birmingham, England.
"I think Ronaldo is a goal-scoring phenomenon. He does lots of things that great players do, but he also does lots of things that great players would never do.
"Getting on to his team mates, complaining to the referee, not chasing back. In one or two of the matches in the European Championship he was outstanding, but in the big matches he was non-existent," said Giles.
"But with Messi, I'd have no doubt - with his attitude and his ability, I'd put him in as one of the greats, up with the best of them. He plays for the team, works for the team."
Generally accepted as one of the few great footballers Ireland has produced, Giles joined Manchester United in 1956 at the age of 15 and formed part of the famous 'Busby Babes' side, much of which was wiped out in the Munich air disaster of 1958.
Manager Matt Busby later remarked that not recognising Giles' potential as a midfielder and letting him leave for Leeds, where he would go on to win two league titles, was the biggest mistake of his career.
Giles has always tried to differentiate between the merely exceptional and the true greats in soccer and his new book "The Great and the Good" is the result of a lifetime of watching, discussing and defining what makes great players.
"When I moved to England I'd speak to some of the older people who'd played against Wilf Mannion and Tommy Lawton and Len Shackleton, but I never got any satisfactory answers," he said.
"They'd say 'he was a great player', or 'he was a character', and I'd ask 'yes, but was he any use?'
"So what I'm trying to do is give the reader an analysis of great players, and hopefully answer the questions that I didn't get any satisfactory answers to."
It was when writing his autobiography "A Football Man" that Giles realised he might have something to contribute to the greatness debate.
During his career he played with or against the likes of Bobby Charlton, George Best, Maradona, Johan Cruyff and Franz Beckenbauer.
In all cases, Giles says he immediately saw what set them apart.
"You know at the time, but you don't stand there admiring them, you're looking to beat them. What you want to do is compete against them. I would respect them, but I'd never be overawed by them."
Asked for a definition of what makes a player great, Giles sums up his answer in one simple word: "Effect".
"What effect do they have on the pitch? There are so many different kinds of players. I described Bobby Charlton as the best player I ever played with or against, but I also describe Roy Keane as a great player," he said.
"Those two have totally different attributes - Keane because of his attitude, his desire, his leadership, whereas Bobby would have been a classical midfield player, distributing the ball, scoring goals."
Now a broadcaster, Giles is still revered in his native country. He amassed 59 caps for Ireland, many as player-manager, and was something of a combination of Charlton and Keane - technically gifted, but never one to shy away from a hard tackle.
He has little time for selfishness on the field. Those who are not prepared to roll up their sleeves in the tough times have little chance of impressing him.
"In my day, we called those players 'sunshine boys' - someone who, when you're winning 3-0, wants the ball all the time. When you're losing 1-0 in a tough match, they turn their back on it," he said.
Giles acknowledges it is usually the goal-scorers that are the greatest players.
"Goal-scoring is the hardest of the lot. It's easier to be a great defender than a midfield player or a forward. Bobby Moore and Franz Beckenbauer were great players and they were defenders," he said.
"But Pele would be able to play much better at left back than Roberto Carlos could up front."