Manchester City boss Roberto Mancini says it has been a great honour to battle with rival manager Alex Ferguson over the last three years as the Italian paid tribute to the United chief on Friday.
Ferguson announced on Wednesday that he will walk away from Old Trafford at the end of this season after almost 27 years in charge, and Mancini praised his foe after three years of the pair battling it out for the Premier League and other major honours in England.
"It is his decision," Mancini, who also revealed he sent Ferguson a message following the news, said.
"For me, it has been a great honour and pleasure to compete against Sir Alex for three years. It was a great honour to beat him in Old Trafford and I wish him good luck for his future. I don't know for which reasons (he is retiring).
"He's a top manager but he took this decision and we should respect it.
"This is difficult (to say who is the best manager). Everyone can have his opinion but one manager who stays for 27 years in the same club and won every trophy for 27 years is an incredible situation.
"I don't think there will be another manager like him, In Europe, there are other good managers. I don't know if you can say Sir Alex is the best (ever) but he is the best in the last 27 years."
David Moyes will replace Ferguson at Old Trafford and Mancini dismissed concerns that the change could hinder United's ability to challenge for major trophies.
When asked if there could be a change at Old Trafford, he said: "I don't think this. A top club, a big club like United, you can change the manager. Sir Alex built this team but it is a big club with a big history and I don't think it will change something."
Mancini's side play Wigan in Saturday's FA Cup final at Wembley and, beyond earning City their third trophy in as many years, victory would also ensure Moyes' first competitive game as United boss would be against the Blues in August's Community Shield.
While some believe the FA Cup has lost its magic in recent years, Mancini does not agree and insists it is important for City to win the trophy after failing to retain their Premier League title.
"It is very important because it is a final, the second final in the last three years. It is important for us and the club," he said.
"When you start the season you want to win the best trophies and more every year but it is not always possible. To get to this final, we have had a good season but not like last season where we won the Premier League.
"I think it is the second trophy in England after the Premier League and an important trophy for everyone. It is a chance to get another Cup and we want to do a good job."
City, who defeated Stoke City 1-0 in the 2011 final, are the clear bookmakers' favourites to beat Wigan but Mancini is not taking the opposition lightly despite the Latics' struggles in the Premier League.
Wigan go into their first FA Cup final three points from league safety with just two games of the season remaining.
"I don't think in the final there is one favourite," he said. "We had problems in the last final, Stoke played very well. To play the FA Cup final in Wembley is different.
"I think that the final is the final, it is not important what can happen in the Premier League.
"After (the final) I think they have a chance (to stay up) because they have two games to stay in the Premier League. Also, (Roberto) Martinez is a very strong manager."