Sir Alex Ferguson is one of the most successful and greatest football managers of all time. He led Manchester United to 38 trophies in 26 years before retiring in 2013, as per BBC Sport. Sir Alex's trophy cabinet includes 13 English Premier League titles, five FA Cups, four league cups, 10 community shield and two UEFA Champions Cup trophies.

In his new book "Leading," which was released this week, the 73-year-old legend has some revelations about his players and his list of possible successors in 2013. "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: Cantona, Giggs, Ronaldo and Scholes. And of the four Cristiano was like an ornament on the top of a Christmas tree," he said as quoted by The Daily Mail.

"They made the difference and the evidence is there. When we brought 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," Sir Alex Ferguson said via ESPN.

"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," he added.

Notable omissions from his list of United players include David Beckham, Rio Ferdinand, Roy Keane, Wayne Rooney, Peter Schmeichel And Carlos Tevez. The 13-time Premier League winner said that these are great players but unlike the four he chose, elevated themselves above all.

He also had an opinion on today's world-class players via The Daily Mail. He said, "In my book there are only two world-class players playing today: Lionel Messi and Cristiano Ronaldo." The manager also revealed the list of managers that were all considered as his successor in 2013 before David Moyes, who was dismissed just after ten months.

Sir Alex said that former Real Madrid boss Carlo Ancelotti, ex-Borussia Dortmund coach Jürgen Klopp, Chelsea manager José Mourinho and current United boss Louis van Gaal were all considered for his position in 2013. Another name he mentioned was incumbent Bayern Munich manager Pep Guardiola.

"I admired Pep greatly. I asked Pep to phone me before he accepted an offer from another club but he didn't and wound up joining Bayern Munich in July 2013," the two-time Champions League winner said. He also revealed that they had a meeting in New York City in 2012 while Guardiola was on a sabbatical, as per another report from BBC Sport.