London - Arsenal boss Arsene Wenger has insisted long-time rival Alex Ferguson's decision to retire as Manchester United manager was no surprise to him.
Ferguson, 71, announced last week he would retire at the end of this season after more than 26 years, and 38 trophies won, at Old Trafford.
He bows out with United having regained the Premier League title and will be succeeded after the end of the current campaign by David Moyes, presently manager of Everton.
Wenger and Ferguson had an especially fiery relationship during the late 1990s and early 200s when their two clubs were contesting the Premier League title although passions have cooled during Arsenal's ongoing run of eight years without a trophy.
The Frenchman said he had long suspected this would be the 71-year-old Ferguson's final season in charge of United.
"I told my staff a long time ago I think that it will be Alex Ferguson's last year, so I was not completely surprised," said Wenger, who talked directly to Ferguson in pre-season as the Scot looked to push through then Arsenal striker Robin van Persie's 24 million move to United
"I detected a few signs through the season, there was already one of them before the season started, that it could be his final year," Wenger added on Monday.
"You have to respect his decision. It is sad because it is the end of a remarkable career. He got a lot of praise that he deserves.
"After 26 years, he just won the championship, he knows it will be more difficult even for Man United to have that consistency now because there are so many teams who have financial power.
"Even for Man United it will be difficult to have the consistency there that they had until now.
"There is a double challenge now, the first is for Manchester United to replace a guy of that stature, and the second challenge for Alex Ferguson to have a life as passionate and as interesting as the life he had until now, but you have to respect the decision."
Wenger is in line to replace Ferguson as the longest-serving manager in the Premier League after taking charge of Arsenal in 1996.
However, the 63-year-old has yet to commit his future to the north London club beyond the end of next season.
Arsenal's lack of silverware since they won the 2005 FA Cup has been a running sore while this season their customary Champions League place has come under threat from local rivals Tottenham Hotspur.
Wenger will next season become the longest-serving manager in the country after taking charge at the Gunners in 1996, but has yet to commit his long-term future past the end of next season.
"I have the luck to be at this club for a long time because I have the faith of my directors and I am grateful for that," said Wenger, whose side face FA Cup winners Wigan in the Premier League at the Emirates on Tuesday.
He added: "I am against (short-termism) because I believe stability is needed inside the clubs for people who represent the values that a club wants to carry though.
"Inside the club it is important to have people who represent these values.
"The manager can be one of these people if he has been there a long time," said Wenger, who reiterated his faith in Arsenal's prospects.
"We have rebuilt the team and since January we have certainly done very well if you look at the number of points we have taken compared to the other teams," he said.
"We have created a good basis and that stability can help us start strongly next season."