Arsène Wenger "was not surprised" to hear of Sir Alex Ferguson's decision to retire as manager of Manchester United and suggested he knew the Scot would quit at the end of this season when United decided to sign Robin van Persie from Arsenal last summer.

Speaking for the first time since his long-time adversary announced his decision to step away from management following 27, trophy-laden years at Old Trafford, Wenger said: "I was not surprised and I told my staff a long time ago that I think it will be Alex Ferguson's last year. 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."

The Frenchman was then asked if Ferguson's retirement was discussed during the negotiations that led to Van Persie's £24m transfer last August and, after smiling coyly, he replied: "I wouldn't like to come back on that. I will let you know one day."

That answer pointed towards the "sign" Wenger had seen, with regard to Ferguson's retirement, prior to the start of this campaign. The deal certainly raised some eyebrows at the time given the expensive capture of a 29-year-old went against United's policy of not spending a significant amount of money on players in the final stages of their career. Ferguson, Wenger may have been suggesting, pursued the deal as part of a short-term plan to regain the Premier League title from Manchester City before he walked away.

Wenger also praised Ferguson for his "remarkable career" at United but expressed concerns that having been involved in football for such a long time, the 71-year-old may find life away from the spotlight difficult to adjust to. "There is a double challenge now," he said. "The first is for Manchester United to replace a guy of that stature, and the second challenge for Alex Ferguson is to have a life as passionate and as interesting as the life he had until now.

"He is luckier than me because he likes horses, he likes golf, so he can certainly have an interesting life again. But of course when you have been such a long time involved in every [game] … our job is always looking forward to the next game, so you are always motivated by that. At the start it is difficult to miss that."

He added: "But 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. You have to respect his decision."