Sir Alex Ferguson 'turned Manchester United into the biggest club in the world', Clayton Blackmore told Sky Sports News HD.
On Wednesday morning the legendary Scottish manager, 71, announced he will retire at the close of the current season, bringing to an end an unprecedented era of success, which has seen Ferguson lead the Old Trafford outfit to 13 Premier League titles, two Champions League wins and five FA Cups.
Blackmore paid tribute to Ferguson's work at United - which began in 1986 - and said English football would never see a manager match his achievements.
"It's a sad day for me and for every Manchester United fan around the world," Blackmore said on hearing the news.
"Ferguson has been here 27 years and he's turned the club from a middle of the league team to probably the biggest team in the world; we win stuff every year here now.
"I was crossing my fingers and hoping he wasn't going to retire but he's got to the stage where he needs to sit back and enjoy all the success he's had at the club.
"Twenty-seven years: you're never going to see that ever again; that has never happened before and it will never happen again.
"It's unbelievable what he's done to the club. He had to fight and scrap in the early days but he turned it around and he keeps producing team after team - and the success he has had is frightening."
Asked about the secret to Ferguson's success at United, Blackmore pointed to the former Aberdeen and Scotland manager's determination to win as his driving force.
"He's strong willed," said Blackmore.
"Everybody hates losing but I've never seen anyone hate losing as much as the manager.
"He instilled that in everybody at the club; anybody who comes into the club has to be a winner, otherwise you're not at the club for too long.
"He was fair, as well. And that's all you need from a manager. He treated you as part of his family. After the game he might give you the hairdryer but two hours later he'd put an arm round you.
"That's why he was in control of his players. Most managers are not really in control of their players but he was."
Blackmore says he now wants to see Ferguson involved in the appointment of his successor and hopes he will stay on at the club to help bed-in the man who has the task of taking up the Manchester United reins.
"The manager should have a say in who succeeds him," said Blackmore.
"I'm hoping he'll be there to help him and tell him how the club's been run over the last 27 years.
"His experience is second to none so we need him to still be there helping the next manager."