Ferguson led United to 13 league titles, two Champions League crowns, five FA Cup victories and four League Cup triumphs in his 27 years at the Old Trafford helm.

Mourinho oversaw two Premier League titles, two League Cup victories and one FA Cup win in his first Chelsea stint, but ended his first campaign back at the Blues empty-handed last season.

Redknapp will take his QPR side to Stamford Bridge on Saturday firmly in the belief that Spain hitman Diego Costa’s signing tipped the title balance in Chelsea’s favour even before a ball was kicked this term.

“He’s proven he’s a fantastic manager wherever he has been: you don’t go and win European Cups like he has unless you’re a top manager,” said Redknapp of the 51-year-old, who led Porto and Inter Milan to Champions League success.

“He has top players and he knows how to get the best out of them and put teams together.

“He’s going to be in the game for many years to come and he could end up as the greatest manager of all time.

“He’s got a charisma about him and has got a great knowledge of the game; he’s been excellent, I couldn’t fault him.

“I absolutely think he can do what Fergie did at Manchester United.

“If he wanted to stay at Chelsea for the next 15 years he could do it; he’s only going to be successful there.

“He’s at the right club with the right chairman.

“It’s very difficult to win anything without money now.

“We all watched TV last year and said how we’d love Diego Costa, but you can’t get him.

“Once he went to Chelsea they were my title favourites.

“When Van Persie went to United two years ago I said they were certs for the league because he was right in his prime.”

Revealing he thought he had convinced Eden Hazard to join Tottenham before he left Lille for Chelsea, Redknapp maintained managers at smaller clubs face tougher tasks.

“At the moment I think staying up with QPR is the tougher challenge (than winning the league with Chelsea),” said Redknapp.

“Every year I look at the manager of the year awards. When I see the people who win it at the big clubs I think it should be given to a Tony Pulis or a Steve Bruce.

“There are probably only four runners for the league at the start of every year.

“I tried to get Hazard at Tottenham, I spent four hours with him in a hotel in Paris talking to him about Tottenham.

“He went to Chelsea not long after, but I thought he was dead keen to come at that time.

“Joe Cole said he was the best player he’d ever played with.

“We pushed for him at the time but we couldn’t get it over the line; it’s the Champions League, it’s such a big draw.”