O’Neill said: “When people talk about modern day managers it is my own belief that he is the greatest in the game going back to when he took over at Manchester United.

“His record at Aberdeen for a provincial club, beating the Old Firm and taking the championship, was fantastic and he has gone on to prove himself at Manchester United.

“I know people think that he was a game away from getting the sack with that famous game at Nottingham Forest.

“But he turned that around with an unbelievable reign. It is an absolutely fantastic achievement to win the championship with any players but he has done it again and again despite having to change his side around with evolution.

“He has had great confidence to change it with the emergence of Paul Scholes, Ryan Giggs and the rest.

“They won the championship again and his record has just been fantastic at a club the size of Manchester United.

“He is coming up to his 1,000th game in charge of the club and it is an absolutely remarkable achievement – and then you throw the Champions League and other successes in for good measure.

“I have the utmost admiration for him, and more than that, and I speak for every manager in European football.”