Sir Alex Ferguson is arguably the greatest manager of all-time.
The Scotsman had incredible success throughout his career but undoubtedly his most fruitful spell came at Manchester United.
Ferguson spent 27 years as boss of The Red Devils and won 38 trophies, including 13 Premier League titles and two Champions League's.
Ferguson managed so many legends during his stint at the club.
But, perhaps surprisingly, Ferguson thought only four of the players he managed at Man Utd were genuinely world-class.
The definition of the word 'world-class' differs from person-to-person and the 79-year-old is very strict when attributing the term.
"There are only two world-class players playing today: Lionel Messi and Cristiano Ronaldo,” Ferguson wrote in his 2015 book 'Leading', per the Independent.
"I don't mean to demean or criticise any of the great or very good footballers who played for me during my 26-year career at United, but there were only four who were world class: [Eric] Cantona, [Ryan] Giggs, [Cristiano] Ronaldo and [Paul] Scholes.
"And of the four Cristiano was like an ornament on the top of a Christmas tree."
Ferguson later said in an interview with the BBC: "They made the difference and the evidence is there. When we brought him [Cantona] in we won the league that season - it was his mere presence and his ability to make and score goals."
"The younger breed like Ryan and Scholes were just fantastic players and the thing about those two was longevity.
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"Are there players who have played right through the whole of the Premier League and performed at the level they have? There are none, absolutely none.
"Of course Ronaldo was just a complete genius of a player."
Ferguson went on to say that Wayne Rooney, David Beckham, Roy Keane, Carlos Tevez, Rio Ferdinand and Peter Schmeichel were all "great players", but refrained from branding them world-class.