Former Manchester City and Newcastle boss Kevin Keegan has hailed old rival Sir Alex Ferguson as the greatest football manager of all time ahead of the Scot's impending retirement from the game.
The pair have enjoyed some memorable managerial duels, notably when Keegan's Newcastle were edged to the Premier League title by Manchester United in the 1995-96 season.
And the ex-England boss believes what Ferguson, who announced on Thursday that he will retire from the game after 26 years at the Old Trafford helm, has achieved will be unsurpassable.
"For me, he's the undisputed greatest football manager the game has seen," Keegan told ESPN. "No-one will achieve what he has done again. It's impossible the way football is going and to be honest almost impossible where it's been.
"If someone had told you 26 years ago that he would go on and build what he has, you'd have laughed them out of town. With all the clubs around at that time, the likes of Liverpool, Arsenal and Everton, the thought of Manchester United becoming such a dominant force would have been ridiculous.
"I wish him a really happy retirement, no-one deserves to enjoy their retirement more than him for everything he has put in to football. I think he'll miss it and the game will miss him."
Although Keegan suffered disappointment at the hands of Ferguson, he also guided Manchester City to their first Premier League victory over United, in the last ever Manchester derby at Maine Road.
But there is one result he remembers with particular fondness.
"We had some great battles over the years, but my favourite memory is definitely when my Newcastle side beat Man United 5-0 [in October, 1996] ," Keegan said. "I'll take that result with me and I know Sir Alex won't begrudge me that!"